Journal of Animal Science

Guthrie, H. D.

doi: 10.2527/2005.8313_supplE79xpmid: N/A

Abstract The predominant pattern of follicle development in pigs is characterized by continuous activation, slow growth to the antral stage, and rapid growth to 4 to 5 mm followed by atresia. The only time that this pattern is broken is when a small portion of the follicle population is selected for ovulation. The mechanisms that regulate the selection of ovulatory follicles are not well understood. However, the ovulatory cohort shifts from FSH to LH dependence at the expense of the nonovulatory follicles as indicated by the following: 1) decreased secretion of FSH, and 2) decreased expression of the FSH receptor and increased expression of the LH receptor. The selection of ovulatory follicles may be dependent on the interaction of members of the intraovarian IGF system to maintain a high level of IGF-I bioavailability. The maintenance of a proliferating population of antral follicles is critically dependent on circulating FSH. A naturally or experimentally induced increase in circulating FSH levels results in an increase in antral follicles; conversely, decreased secretion of FSH is followed by a decrease in the number and in health status of antral follicles. Gonadotropin treatment with eCG or PG600 triggers selection of ovulatory follicles, and although these treatments do not increase litter size, they are beneficial for treatment of anestrus and, in conjunction with hCG or GnRH analogs, provide better control of the time of ovulation. The use of porcine FSH has not increased ovulation rate or improved oocyte developmental competence. To improve reproductive efficiency in the future, research should be directed toward obtaining more knowledge about genetic and physiological regulation of ovulatory follicle selection and the effect of follicle development on oocyte developmental competence. Introduction Antrum formation is the stage of development in which follicles become dependent on the secretion of pituitary gonadotropins (Fortune, 1994; Burns and Matzuk, 2002). After activation, follicles grow slowly to the antral follicle stage and then undergo a relatively short burst of cell proliferation (Hirshfield, 1991; Morbeck et al., 1992; Fortune, 1994). Most antral follicles die, but once during each estrous cycle, a small portion of the population is selected for ovulation. Based on estimated growth rates in colchicine-arrested prepubertal gilts, once activated, a follicle requires 84 d to reach the antral stage (Morbeck et al., 1992). Growth of newly formed antral follicles (400 μm to 3 mm) was calculated to require 2 wk, and when follicles grew to ovulatory size, five additional days were required. From their estimate of antral follicle growth rate, Morbeck et al. (1992) hypothesized that the follicles undergoing antrum formation at the beginning of the cycle reach 3 mm in diameter on d 14 to 16 of the estrous cycle and constitute the population from which the ovulatory follicles are selected. A better understanding of factors and molecular mechanisms of folliculogenesis could enhance our ability to produce developmentally competent oocytes either in vivo or in vitro. Estrous Cycle: Follicle Population and Endocrine Changes The populations of small (1 to 2 mm) and medium (3 to 5 mm) follicles essentially disappear during the follicular phase of the cycle as the ovulatory follicles mature (Foxcroft and Hunter, 1985; Guthrie et al., 1995). The depleted follicle populations are replenished after ovulation with small follicles restored to 35 to 40 per animal by d 2 and medium follicles restored to approximately 40 per gilt by d 8 of the cycle. During the first 5 d of the cycle, 95% of the small and medium follicles are healthy (nonatretic) and steroidogenically active (Guthrie et al., 1995; Garrett and Guthrie, 1997). However, by d 7, the level of atresia increased to 50%, and steroidogenesis and granulosa cell proliferative activity were declining. Hirshfield (1991) suggested that as growth continues, the follicle wall reaches a certain thickness, which becomes limiting with respect to gas and nutrient exchange in the membrana granulosa. At this point, cell proliferation slows and cells begin to die. Perhaps porcine follicles grown after ovulation have reached their limit of growth as d 7 approaches and are beginning to die. This process of growth and death is a continuous process; only those follicles positioned in the window of opportunity opened by progestin withdrawal escape this fate and undergo preovulatory maturation. Whether groups of antral follicles grow to medium size in a few successive waves beginning after ovulation or grow more or less continuously throughout the luteal phase is unknown. The FSH secretory pattern during the 41 h before recovery of follicles for analysis on different days during the luteal phase was not significantly correlated with follicle size distributions, atresia status, or intrafollicular steroid hormone concentrations (Guthrie and Cooper, 1996). The high circulating progesterone concentrations established during the first week of the estrous cycle persist until approximately d 12 to 14 of the cycle (Guthrie and Bolt, 1983, 1990; Knox et al., 2003), when progesterone secretion decreases to mark the onset of luteolysis. The development of large follicles and the diminished numbers of small and medium follicles during the follicular phase are accompanied by a dramatic decline in circulation levels of FSH (Guthrie and Bolt, 1983, 1990; Knox et al., 2003) starting approximately 1.5 to 2 d after the initiation of the decline in circulating progesterone. During the transition from the luteal to the follicular phase, circulating levels of LH seem to shift from a luteal-phase pulsatile mode to a follicular-phase mode characterized by a decrease in the incidence of pulsatile secretion and in the mean concentration until the preovulatory surge (Guthrie and Bolt, 1990; Flowers et al., 1991; Guthrie et al., 1993, 1997). The first indication of follicle maturation in the pig, increased ovarian secretion of estradiol-17β into the ovarian vein, occurs in conjunction with decreasing progesterone in the absence of any significant change in plasma LH secretion pattern or concentration (Flowers et al., 1991). If LH secretion does not increase during the early follicular phase, then follicle maturation may result from a change in the balance between progestin and gonadotropin action at the ovarian level. The notion of progesterone playing a direct role in suppressing follicle development is supported by the suppression of large follicles (Guthrie et al., 1995) and steroidogenesis, including estradiol-17β, in healthy follicles during the luteal phase of the estrous cycle (Guthrie and Cooper, 1996), and by the fact that progesterone added to cultured granulosa cells of prepubertal gilts (Chan and Tan, 1986) antagonizes the stimulatory effect of gonadotropins on estrogen production. The subsequent decrease in circulating levels of FSH and LH during the follicular phase is postulated to be the result of inhibin and estradiol negative feedback at the anterior pituitary and hypothalamus, respectively (Guthrie et al., 1995). Gene Expression During Follicular Phase For the purpose of discussion, the follicular phase of cyclic gilts and weaned sows will be divided into different days or stages as illustrated in Figure 1. The first stage, d 1, represents the late luteal phase or prefollicular phase stage of development corresponding to 24 h after the last feeding of altrenogest (d 0) or 24 h after weaning. Days 3 and 5 represent progressive stages of preovulatory maturation before the preovulatory LH surge, and d 7 represents terminal differentiation, 24 to 36 h after the onset of the preovulatory LH surge. Figure 1. View largeDownload slide The shift from FSH to LH dependence during the follicular phase of the estrous cycle. Panel A shows the decreasing plasma FSH concentration between d 1 and 5 (modified from Guthrie et al., 1993). Panel B shows decreasing expression of FSH receptor (FSHR) mRNA and increasing expression LH receptor (LHR) and aromatase (P450arom) mRNA (modified from Liu et al., 2000). Means for P450arom, FSHR, and LHR with no common superscript letter differ (P < 0.05). Figure 1. View largeDownload slide The shift from FSH to LH dependence during the follicular phase of the estrous cycle. Panel A shows the decreasing plasma FSH concentration between d 1 and 5 (modified from Guthrie et al., 1993). Panel B shows decreasing expression of FSH receptor (FSHR) mRNA and increasing expression LH receptor (LHR) and aromatase (P450arom) mRNA (modified from Liu et al., 2000). Means for P450arom, FSHR, and LHR with no common superscript letter differ (P < 0.05). A major event associated with the selection of ovulatory follicles is the shift in follicle dependence from FSH to LH. Two physiological events result in a reduction in the bioavailability of FSH to preovulatory follicles. Circulating levels of FSH decrease by four- to fivefold between d 1 and 5 of the follicular phase after cessation of altrenogest administration (Guthrie et al., 1993) or following luteolysis (Guthrie and Bolt, 1983; Knox et al., 2003), as illustrated in Figure 1A. In addition, FSH-receptor (FSHR) mRNA expression in granulosa cells of small and medium healthy follicles also decreases between d 1 and 5 (Figure 1B) to very low levels (as measured by northern and RNase protection analysis) within hours of the expected preovulatory LH surge (Liu et al., 1998, 2000). The shift to LH dependence is indicated by increased expression of LH receptor (LHR) mRNA in granulosa and theca interna cells between d 1 and 3, and is greatest in granulosa and theca interna cells of large follicles, especially in granulosa cells on d 5 (Figure 1B). The changes in FSHR and LHR expression are positively associated with the function of FSHR and LHR during preovulatory follicle maturation. The loss of FSH response and the increase in LH response in porcine granulosa cells during preovulatory maturation in terms of adenosine cyclic 3′,5′-phosphate production in vitro and the relative number of FSH and LH binding sites (reviewed by Ainsworth et al., 1990) are in general agreement with the expression pattern of the FSHR and LHR mRNA in vivo. In addition, the shift to LH dependence may begin much earlier in the estrus cycle of the pig. Histological examination of follicles in hypophysectomized gilts, intact gonadotropin-releasing hormone inhibitor treated gilts, and intact control gilts indicated that development of healthy follicles 1.1 to 2 mm in diameter was FSH-dependent, whereas those >2 mm in diameter were dependent on LH pulsatile secretion (Driancourt et al., 1995). The nature of follicle growth also changes during pre-ovulatory maturation. Cell proliferation slows in healthy follicles as they became estrogen active (>100 ng/mL of estradiol) and increase in size >5 mm (Fricke et al., 1996; Garrett and Guthrie, 1997). The selected follicles continue to increase in size, but growth is primarily due to an increase in follicle diameter through accumulation of fluid. Granulosa and theca cell proliferation continue at a rate just sufficient to maintain the thickness of the follicle wall until proliferation is completely arrested after the preovulatory LH surge (Fricke et al., 1996). The intrafollicular concentration of estradiol-17β is a well-established marker for preovulatory maturation and is closely correlated with expression of aromatase (P450arom) mRNA (Guthrie et al., 1994) and protein (Garrett and Guthrie, 1997). The expression of P450arom (Figure 1B) is maximal in large follicles on d 5 and decreases on d 7. Many genes that may play a role in preovulatory maturation are expressed in the ovarian follicle in a pattern similar to that of P450arom; inhibinα, inhibin/activin β A (Guthrie et al., 1992; Li et al., 1997), P45017α (Guthrie et al., 1994; Liu et al., 2000), LHR (Liu et al., 2000), IGF-I (Samaras et al., 1993), and IGF-II (Liu et al., 2000) increase to a maximum on d 5 in large follicles and then decrease by varying degrees between d 5 and 7. The increase in expression of steroidogenic enzymes is associated with an increase in LHR mRNA in both granulosa and theca interna cells. Experiments in LHR knock-out (KO) mice have shown that the expression of these enzymes and of the ovulatory process are dependent on the action of the LHR (Burns and Matzuk, 2002). Role of IGF System in Selection of Ovulatory Follicles Insulin-like growth factors and low-molecular-weight IGFBP are considered as stimulators and inhibitors, respectively, of follicle growth and maturation (see reviews of Hammond et al., 1993; Mazerbourg et al., 2003). The IGF system comprises two ligands, IGF-I and IGF-II; two receptors, the type I receptor (IGFR) and the type II/mannose-6-phosphate receptor, and six IGFBP, which bind IFG-I and IGF-II with high affinity. The low-molecular-weight IGFBP (ranging from 24 to 35 kDa) include IGFBP-1, -2, -4, -5-, and -6, which are present in variable proportions in the follicular fluid of different species. Ovarian IGF-I plays a critical role in folliculogenesis after the early antral stage (Mazerbourg et al., 2003). The KO of IGF-I in the mouse exhibit normal activation of primordial follicles and produces normal numbers of granulosa cells in preantral follicles (Baker et al., 1996). However, growth of antral follicles and ovulation do not occur even with gonadotropin replacement therapy. In contrast, growth of antral follicles and ovulation in IGF-I KO mice can be restored after 2 wk of exogenous IGF-I replacement (Zhou et al., 1997). The interaction of IGF-I and FSH in the development of antral follicles is quite complex. Expression of FSHR mRNA is depressed in the IGF-I KO, whereas full expression of IGF-I mRNA was found in FSHR KO (Zhou et al., 1997). These results indicate the hierarchy of control between these two genes, such that IGF-I serves to permit and augment the physiological responses of granulosa cells to FSH by induction of the expression of the FSHR. The FSHR is required for expression of other genes important for antral follicle growth, such as P450arom (Zhou et al., 1997), inhibin α and β subunits, and LHR (Burns and Matzuk, 2002). In the pig, the hierarchy of importance for IGF-I and the FSHR is uncertain because transcripts for IGF-I and FSHR are present even in the primary follicles of mature gilts (Yuan et al., 1996). Abundant IGF-I mRNA is present in granulosa cells as well as theca externa cells during the follicular phase (Liu et al., 2000). The amount of IGF-I mRNA in the follicle walls of individual follicles increased (P < 0.001) approximately 4.5-fold between d 1 and 5 (Figure 2A) and is highly correlated with growth (diameter) and estradiol-17β production (log of estradiol-17β concentration); r > 0.7; P < 0.01 (Samaras et al., 1993). Results of other experiments also indicated abundant IGF-I expression, but no effect of follicular stage (follicle size or day), (Liu et al., 2000). As an estimate of IGF-I translational output, follicular fluid IGF did not change significantly between d 1 and 5 (Liu et al., 2000). Granulosa cells express IGFR mRNA in a constitutive pattern, with no differences (P > 0.10) among different stages of development, size, or day (Figure 2A). Figure 2. View largeDownload slide Granulosa cell expression of mRNA of IGF-I and type 1 IGF receptor (IGFR) in panel A and IGFBP-2 and -4 in panel B. Means for IGF-I and IGFBP-2 that do not have a superscript letter in common differ (P < 0.05; modified from Samaras et al., 1993; Liu et al., 2000). Figure 2. View largeDownload slide Granulosa cell expression of mRNA of IGF-I and type 1 IGF receptor (IGFR) in panel A and IGFBP-2 and -4 in panel B. Means for IGF-I and IGFBP-2 that do not have a superscript letter in common differ (P < 0.05; modified from Samaras et al., 1993; Liu et al., 2000). Although the levels of follicular IGF-I protein may or may not change significantly during the follicular phase, its biological availability may be closely regulated by the presence of IGFBP in follicular tissue. Granulosa and theca interna cells expressed IGFBP-2 mRNA (Liu et al., 2000), but expression of IGFBP-2 mRNA is greater in granulosa cells compared with theca cells (P < 0.05). A decrease in IGFBP-2 mRNA expression in the tissue of preovulatory follicles between d 1 and 5 (Figure 2B) supports the notion that the bioavailability of IGF-I increases in the maturing ovulatory follicles (Samaras et al., 1993; Liu et al., 2000.) Expression of IGFBP-4 mRNA seems to be less important as a regulatory factor as its mRNA is present at a much lower level than IGFBP-2 mRNA and did not differ (P > 0.10) among different stages of development (Figure 2B). The major IGFBP in porcine follicular fluid as measured by ligand blotting were IGFBP-3 (43 to 40 kDa) and IGFBP-2 (34-kDa), (Besnard et al., 1997; Liu et al., 2000). Follicular fluid IGFBP-3 was greater (P < 0.01) on d 3 and 5 compared with d 1 and seemed to be associated with preovulatory maturation. The amount of IGFBP-2 in follicular fluid was greater (P < 0.01) on d 1 and 3 than on d 5, and is in agreement with the notion of an increase in IGF-I bioavailability. The IGFBP can inhibit IGF action by sequestration at the site of action because the affinity of IGFBP for IGF is similar to the affinity of the IGFR (Mazerbourg et al., 2003). Further, the affinity of IGFBP-3, -4, and -5 for IGF are decreased when they are proteolyzed. A physiological role for IGFBP in the survival and continued growth of ovulatory follicles is also indicated by a decrease in levels of intrafollicular IGFBP-2 and IGFBP-4. For example, the reduction of intrafollicular IGFBP-2 in the pig is likely due to a combination of decreased transcriptional/translation activity of the gene in follicular tissue as discussed above and to an increase in IGFBP-2 proteolytic degradation found in growing ovulatory follicles (Mazerbourg et al., 2003). In healthy small follicles corresponding to d 1, IGFBP-2 degradation activity is low, with a 30% loss of IGFBP-2 during a 20 h incubation assay (Besnard et al., 1997). However, by d 4 in large follicles, IGFBP-2 degradation activity increased to 80% (Figure 3). Degradation of endogenous IGFBP-2 was lower in atretic vs. healthy follicles (Figure 3). The end result is that during the terminal stages of ovulatory follicle growth, follicular fluids contain low to undetectable levels of native IGFBP-2 as assessed by Western ligand blotting in comparison with the corresponding serum. In contrast, much higher levels of 23- and 12-kDa proteolytic fragments were found by immunoblotting in bovine and porcine preovulatory follicular fluid than in the corresponding serum. Moreover, IGF-I seems to activate a positive feedback loop by increasing the rate of IGFBP degradation in test samples of bovine and porcine preovulatory follicular fluid. Figure 3. View largeDownload slide Effect of follicle size class on the percentage of endogenous follicular fluid IGFBP-2 degraded during 20 h of incubation. Means for healthy follicles that do not have a superscript letter in common differ (P < 0.05), and means for atretic follicles with an asterisk differ (P < 0.05) from those for healthy follicles of same size class (modified from Besnard et al., 1997). Figure 3. View largeDownload slide Effect of follicle size class on the percentage of endogenous follicular fluid IGFBP-2 degraded during 20 h of incubation. Means for healthy follicles that do not have a superscript letter in common differ (P < 0.05), and means for atretic follicles with an asterisk differ (P < 0.05) from those for healthy follicles of same size class (modified from Besnard et al., 1997). Immunoneutralization and immunoprecipitation studies have shown the protease that degrades IGFBP-4, IGFBP-2, and IGFBP-5 in ovine, porcine, bovine, and equine ovulatory follicles is the pregnancy-associated plasma protein-A (PAPP-A), previously identified in human fibroblasts and osteoblasts (Mazerbourg et al., 2003). In support of the physiological role of PAPP-A in the pig, expression of PAPP-A mRNA is lower in atretic and small healthy follicles than in ovulatory follicles (correlation between exogenous IGFBP-4 degradation and PAPP-A mRNA abundance, r = 0.55, P = 0.0016), (Mazerbourg et al., 2001). Those follicles containing high levels PAPP-A mRNA have greater capacity to degrade exogenous IGFBP-4. Experimental Manipulation of Follicle Development A series of experiments will be reviewed to illustrate the role of FSH and eCG in maintaining a population of ovarian follicles from which the ovulatory follicles are selected and to determine whether exogenous FSH might be an alternative method to stimulate follicle growth and increase recruitment or selection of ovulatory follicles. FSH Administration During an Artificial Luteal Phase Cyclic gilts were administered altrenogest to maintain an artificial luteal phase and were treated for 3 d at 8-h intervals with four treatment combinations to decrease or increase circulating levels of FSH: 1) saline and charcoal-stripped porcine serum as a control, 2) saline and charcoal stripped porcine follicular fluid (pFF) as a source of inhibin, 3) USDA porcine FSH (pFSH) and serum, and 4) pFSH and pFF (Guthrie et al., 1988). This FSH preparation was considered to be free of LH activity, with <1% contamination based on ascorbic acid depletion assay and a very low level of LH displacement in a luteal tissue LHR assay (Guthrie et al., 1990). The results of this experiment are summarized in Figure 4A and B. The number of small and medium follicles in the saline + serum control gilts, 53 and 31 per gilt, respectively, were similar to the numbers that would be found during the midluteal phase of the cycle. Administration of saline + pFF caused a decrease (P < 0.05) in circulating levels of FSH compared with gilts injected with saline−serum and decreased (P < 0.05) the number of medium follicles compared with saline + serum to 0.8 per animal. Injections of FSH + serum increased circulating levels of FSH compared with saline + serum, and increased (P < 0.05) the number of medium follicles to 57 per animal without a significant effect on the number of small follicles. The combination of pFSH + pFF also increased circulating FSH levels and increased (P < 0.05) the number of medium follicles compared with saline+pFF, in effect, restoring the population to a distribution similar to that in the control gilts. In another experiment, within 48 h after initiation of pFF injections, follicles were atretic by morphological criterion being opaque in appearance and containing cellular debris (Guthrie et al., 1987). From these experiments, we concluded that changes in circulating FSH over a 3-d interval were closely coupled to changes in follicular growth during the same period of time. The surprising result was that the pFSH treatment did not result in development of large, estrogenic follicles or increased secretion of estradiol-17β. In contrast, a single injection of eCG induced growth of large, estradiol-17β-secreting follicles during an artificial luteal phase induced by altrenogest, and a subsequent injection of hCG was capable of ovulating these follicles (Guthrie and Bolt, 1985). Figure 4. View largeDownload slide Effects of injections at 8-h intervals of charcoal-stripped porcine serum or follicular fluid (pFF) and saline or porcine FSH (pFSH) 72 h after the first injection on the number of small, medium, and large follicles (A) and on the linear regression of plasma FSH concentration on time (B) in postpubertal gilts treated during an altrenogest artificial luteal phase. Means for the number of 4-to 6-mm follicles and FSH regression coefficients that do not have a superscript letter in common differ (P < 0.05; modified from Guthrie et al., 1988). Figure 4. View largeDownload slide Effects of injections at 8-h intervals of charcoal-stripped porcine serum or follicular fluid (pFF) and saline or porcine FSH (pFSH) 72 h after the first injection on the number of small, medium, and large follicles (A) and on the linear regression of plasma FSH concentration on time (B) in postpubertal gilts treated during an altrenogest artificial luteal phase. Means for the number of 4-to 6-mm follicles and FSH regression coefficients that do not have a superscript letter in common differ (P < 0.05; modified from Guthrie et al., 1988). Gonadotropin Administration to Prepubertal Gilts The results of the experiments described in the previous section indicated that whereas pFSH treatment induced growth of medium size follicles, it did not induce development of estrogen active large follicles during an altrenogest artificial luteal phase. To further characterize the effect of pFSH in a different experimental model, free of a possible progestin antagonism, an experiment was conducted in prepubertal gilts. Crossbred gilts at 160 d of age were injected 1) once with saline, 2) nine times at 8-h intervals with USDA pFSH; or 3) once with 15 IU/kg BW of eCG (Guthrie et al., 1990). Plasma was collected during the 72-h treatment period and ovaries were collected at slaughter 72 h after the first injection. The saline-injected gilts contained essentially no large follicles, and the numbers of small and medium follicles were 104 and eight per gilt, respectively. Injections of gonadotropins caused radical shifts in the distribution of follicles in these size classes (Figure 5A). Compared with saline, the 3-d exposure of ovaries to FSH treatment increased (P < 0.05) the number of small follicles to 152 per gilt, but had no significant effect on the number of medium or large follicles. In contrast to pFSH, eCG increased development of large follicles and decreased (P < 0.05) the total number and the number of small follicles compared with saline-injected gilts. The pFSH treatment increased (P < 0.05) plasma FSH concentration, whereas eCG decreased (P < 0.05) FSH secretion (Figure 5B). Secretion of estradiol-17β increased (P < 0.05) only following eCG treatment (Figure 5B), and aromatase activity was induced only in granulosa cells isolated from the follicles of the eCG-treated gilts. The common themes emerging from this work were as follows: 1) FSH plays an important role in the maintenance of a proliferating population of small or medium follicles in sexually mature and prepubertal swine, 2) selection of ovulatory follicles (spontaneous or gonadotropin induced) is accompanied by a decrease in FSH secretion, and 3) pFSH treatment did not induce the growth of large follicles or estradiol production. Figure 5. View largeDownload slide Effects of injections of porcine FSH (pFSH) and eCG at 8-h intervals on the number of 1- to 3- and 4- to 6-mm follicles (A) and on the linear regression of plasma FSH and estradiol concentrations on time (B) 72 h after the first injection in prepubertal gilts. Means for the number of 1- to 3-mm follicles and the linear regression coefficients for FSH and estradiol that do not have a superscript letter in common differ (P < 0.05; modified from Guthrie et al., 1990). Figure 5. View largeDownload slide Effects of injections of porcine FSH (pFSH) and eCG at 8-h intervals on the number of 1- to 3- and 4- to 6-mm follicles (A) and on the linear regression of plasma FSH and estradiol concentrations on time (B) 72 h after the first injection in prepubertal gilts. Means for the number of 1- to 3-mm follicles and the linear regression coefficients for FSH and estradiol that do not have a superscript letter in common differ (P < 0.05; modified from Guthrie et al., 1990). Recently, results were published that described the acute effects of eCG on follicle size distribution and granulosa cell apoptosis in luteal phase gilts (Liu et al., 2003). Injection of eCG (1,000 IU) on d 11 of the cycle caused a dramatic, transient increase (P < 0.05) in the number of small and medium follicles on d 12 followed by a gradual decline to pretreatment numbers on d 13 (Figure 6A). The percentage of apoptotic granulosa cells in small and medium follicles was transiently decreased (P < 0.05) from 20 to 21% on d 11 to 8 to 10% 24 h later and then increased to d 11 levels at 96 h after injection (Figure 6B). The increased number of healthy follicles 24 h after injection may have been triggered by the FSH-like activity known to reside in eCG (Guthrie et al., 1990). The decrease in small and medium follicles and increased granulosa cell apoptosis after d 12 could be a result of 1) decreased secretion of FSH that follows the injection of eCG, 2) the potential decay of follicle stimulating activity in the eCG molecule itself, and 3) the potential atretogenic effect of the LH activity in eCG. The comparison of pFSH and eCG effects on follicular development indicates that the LH activity of eCG or the relatively long half life of eCG might explain the differences in biological effects relative to pFSH in maturation of preovulatory follicles. Figure 6. View largeDownload slide Effects of a single injection of eCG on d 11 of the estrous cycle on the number of <3 mm, 3 to 5 mm, and >5 mm follicles (A) and percentage of apoptotic granulosa cells (GC) in <3 mm, 3 to 5 mm, and >5 mm follicles (B). Means for the number of <3 mm and 3- to 5-mm follicles that do not have a superscript letter in common differ (P < 0.05; modified from Liu et al., 2003). Figure 6. View largeDownload slide Effects of a single injection of eCG on d 11 of the estrous cycle on the number of <3 mm, 3 to 5 mm, and >5 mm follicles (A) and percentage of apoptotic granulosa cells (GC) in <3 mm, 3 to 5 mm, and >5 mm follicles (B). Means for the number of <3 mm and 3- to 5-mm follicles that do not have a superscript letter in common differ (P < 0.05; modified from Liu et al., 2003). Follicular Phase FSH Treatment Treatment regimens such as eGC or PG600 have provided benefit for treatment of anestrus and, in conjunction with hCG or GnRH analogs, provide better control of the time of ovulation and have increased ovulation rate; however, litter size has not been increased. Reproductive efficiency might still be improved with new protocols and management tools to provide for more precise or reliable scheduling of estrus and ovulation. An experiment was performed to compare the effects of pFSH and eCG on follicle development in terms of estradiol-17β secretion, ovulation rate, and fertilization rate (Guthrie et al., 1997). Postpuberal gilts were synchronized using altrenogest and assigned to one of four treatments: 1) one injection of saline (control) on d 1, 2) twice daily injections of Super Ov (Ausa Int., Tyler, TX) at a dose of 2.8 NIH FSH-S1 IU of pFSH/100 kg BW on d 1, 2, and 3, and 3) Super Ov at a dose of 4.6 NIH FSH-S1 IU of pFSH/100 kg BW on d 1, 2, and 3, or 4) one injection of 1,300 IU of eCG on d 1. The gilts in treatments 2 through 4 were artificially inseminated, eggs were recovered surgically 48 h after an injection of hCG, and ovarian structures (corpora lutea and un-ovulated follicles) were recorded. An average of 18 corpora lutea were recorded for the saline, control gilts. Injection of eCG increased (P < 0.05) the number of corpora lutea to 43 per gilt compared with controls. Neither the low nor high dose of pFSH had a significant effect on ovulation rate compared with the saline-injected gilts. The high-dose pFSH seemed to stimulate more follicle growth than low-dose FSH or saline, but only 38% of the follicles ovulated. A greater proportion of the saline- (100%) and eCG-treated gilts (87%) were detected to be in estrus compared with 53.2% for the FSH-treated gilts (P < 0.001). The fertilization rate among the eggs recovered did not differ between the FSH and eCG treatment groups. Analysis of circulating hormone levels showed that plasma FSH increased between d 1 and 4 in the FSH-injected gilts and decreased in saline- and eCG-injected gilts. Plasma estradiol increased between d 1 and 4 in all experimental groups, but the increase in the eCG-injected gilts was greater (P < 0.05) than that for the saline- and FSH-injected gilts. Plasma estradiol profiles did not differ among saline- and FSH-injected gilts. Administration of the high dose of pFSH during the follicular phase stimulated growth of large, estrogenic follicles, but circulating levels of estradiol-17β did not reflect that increased follicle growth. Oocyte Developmental Competence The rationale for the production of so many germ cells during early fetal life and their subsequent loss in pigs and other species is unknown. The importance of apoptosis and follicular atresia may be that after antrum formation, follicles may have a finite life span (Hirshfield, 1991). Generally 50% of antral follicles on the ovarian surface are atretic. The meiotic status of porcine oocytes is very heterogeneous, 70% of oocytes in 3 to 5 mm diameter follicles have initiated germinal vesicle breakdown (GVBD) in prepubertal (Funahshi and Day, 1997; Grupen et al., 1997; my unpublished observations) and postpubertal gilts (Brüssow et al., 1996; Guthrie and Garrett, 2000). The incidence of GVBD did not differ significantly between healthy and atretic follicles before the start of ovulatory follicle maturation. However, follicles containing oocytes undergoing GVBD may be eliminated during the follicular phase because oocytes examined immediately before the preovulatory LH surge were predominantly in meiotic arrest (Hunter and Polge, 1966; Motlik and Fulka, 1976). Therefore, atresia may be physiologically important to eliminate oocytes that are degenerate or have escaped meiotic arrest. The oocytes used for in vitro maturation/fertilization (IVM/IVF) are predominantly from prepubertal gilts. Typically, the IVM period is 40 to 46 h, and it is possible that a subpopulation of oocytes has reached metaphase II by as much as 20 h earlier than the rest. Three approaches have been used to reduce meiotic heterogeneity before the induction of the maturation process: 1) administration of gonadotropins to gilts 72 h before oocyte collection, 2) preincubation of oocytes without gonadotropins, and 3) exposure of oocytes to dibutyryl cyclic adenosine 3′, 5′-monophosphate or hypoxanthine to induce synchronization (Funahshi and Day, 1997). These meiotic synchronization protocols would imply that the GVBD is reversible; however, this reversal in meiotic status requires experimental confirmation. Developmental competence of IVM/IVF oocytes has been investigated following different gonadotropin treatments of prepubertal gilts (Bolamba et al., 1996). The following treatments were assigned to five groups of six prepubertal gilts each: 1) one injection of saline, 2) two injections of 8 mg of pFSH (Schering) at 12-h intervals, 3) 16 mg of pFSH at 12-h intervals, 4) one injection of 1,000 IU of eCG, and 5) one injection of PG600. Gilts were killed to count follicles and recover oocytes for IVM/IVF 72 h after the first injection for each treatment. Additional gilts were treated and killed at 48 h. At 48 h, two significant changes in the follicle population were found. The number of large follicles in the eCG and PG600 groups was already significantly greater than those in the saline group, and the level of atresia in all follicles was 54% for the saline and FSH treatment groups compared with 87% for the eCG and PG600 groups. Administration of FSH-16 tended to increase the total number of follicles per gilt at 72 h, but it did not increase the number of large follicles compared with the saline control group (Figure 7). Treatment with eCG and PG600 decreased the total number of follicles compared with the saline-injected gilts and increased the number of large follicles compared with saline- and FSH-injected gilts. The FSH-16 gilts yielded greater (P < 0.05) numbers of good oocytes (uniform appearing cytoplasm and compact or expanding cumulus cell mass) than the saline, eCG, and PG600 groups (Figure 8). However, this apparent advantage was not maintained when oocytes representing these treatment groups were examined after IVM/IVF (Figure 9). The increased number of good oocytes recovered from pFSH-treated gilts was neutralized by the decreased oocyte developmental competence; the percentage of normal fertilized eggs recovered from eCG and PG600 gilts was 45 to 50% compared with 10 to 12% for pFSH-injected gilts. Figure 7. View largeDownload slide Effect of gonadotropin treatment on the number of small, medium, and large follicles in prepubertal gilts 72 h after the first injection. Treatments were a single injection of saline, injections of Schering porcine FSH at 12-h intervals (8 or 16 mg), a single injection of eCG, and a single injection of PG600. Means for the number of small, medium, and large follicles, and the percentage of apoptotic granulosa cells in small and medium follicles that do not have a superscript letter in common differ (P < 0.05; modified from Bolamba et al., 1996). Figure 7. View largeDownload slide Effect of gonadotropin treatment on the number of small, medium, and large follicles in prepubertal gilts 72 h after the first injection. Treatments were a single injection of saline, injections of Schering porcine FSH at 12-h intervals (8 or 16 mg), a single injection of eCG, and a single injection of PG600. Means for the number of small, medium, and large follicles, and the percentage of apoptotic granulosa cells in small and medium follicles that do not have a superscript letter in common differ (P < 0.05; modified from Bolamba et al., 1996). Figure 8. View largeDownload slide Effect of gonadotropin treatment on number of good and poor quality oocytes recovered from prepubertal gilts 72 h after the first injection. Treatments were as described in Figure 7. Means for the number of good-quality oocytes that do not have a superscript letter in common differ (P < 0.05; modified from Bolamba et al., 1996). Figure 8. View largeDownload slide Effect of gonadotropin treatment on number of good and poor quality oocytes recovered from prepubertal gilts 72 h after the first injection. Treatments were as described in Figure 7. Means for the number of good-quality oocytes that do not have a superscript letter in common differ (P < 0.05; modified from Bolamba et al., 1996). Figure 9. View largeDownload slide Effect of gonadotropin treatment on sperm penetration, polyspermy, and normal fertilization after in vitro maturation and fertilization of oocytes recovered from prepubertal gilts 72 h after the first injection. Treatments were as described in Figure 7. Means for the percentage of normal fertilized oocytes that do not have a superscript letter in common differ (P < 0.05; modified from Bolamba et al., 1996). Figure 9. View largeDownload slide Effect of gonadotropin treatment on sperm penetration, polyspermy, and normal fertilization after in vitro maturation and fertilization of oocytes recovered from prepubertal gilts 72 h after the first injection. Treatments were as described in Figure 7. Means for the percentage of normal fertilized oocytes that do not have a superscript letter in common differ (P < 0.05; modified from Bolamba et al., 1996). Although exogenous gonadotropin treatments did not enhance apparent oocyte developmental competence in vitro, there are some changes in the experimental protocol that could improve the results. The ovarian response to Schering FSH preparations is unpredictable because they are known to contain LH contamination. Although two injections of Schering pFSH did not result in ovulations (Bolamba et al., 1996), additional injections did result in ovulation (Bolamba and Sirard, 2000). Presumably, each injection of Schering pFSH induced development of estrogen active follicles; these follicles may have induced their own ovulation by positive feedback on LH release or alternatively (or simultaneously), the LH activity in this particular FSH preparation itself elicited luteinization and perhaps ovulation. A FSH preparation with a lower LH content should be tested. Other modifications could include collection of oocytes sooner after initial gonadotropin treatment (24 or 48 h) and development of improved IVM protocols. Conclusions The purpose of preovulatory follicle maturation is to provide an environment that ensures delivery of a subpopulation of developmentally competent oocytes and capacitated sperm to the site of fertilization. Follicles selected for ovulation must be at the right place at the right time; a window of opportunity exists on d 14 to 16 of the estrous cycle or following an injection of eCG in prepubertal gilts. To improve reproductive efficiency in the future, research should be directed toward obtaining more knowledge about genetic and physiological regulation of ovulatory follicle selection and the effect of follicle development on oocyte developmental competence. The FSH treatment protocols were not found to be useful as assisted reproductive techniques in swine for the following reasons: 1) the failure to increase ovulation rate, 2) association with a low incidence of estrus compared with eCG treatment, and 3) low in vitro oocyte developmental competence compared with eCG. Implications Increasing ovulation rate and obtaining more precise control of the time of ovulation have been sought after goals for many years. Gonadotropin treatment with equine chorionic gonadatropin or prostaglandin 600 triggers selection of ovulatory follicles. Although these treatments do not increase litter size, they are beneficial for treatment of anestrus and, in conjunction with human chorionic gonadotropin and gonadotropin-releasing hormone analogs, provide better control of the time of ovulation. However, there is still room for more precise timing of ovulation, more reliable estrus detection, and improved oocyte developmental competence (better embryo survival). Follicle maturation itself has been investigated by cell culture and by analysis of tissues and blood plasma recovered at different stages of development. Treatments of a stimulatory and inhibitory nature have been applied in vitro and in vivo. These approaches have been valuable in generating a physiological database; however, there are still massive gaps in our understanding of recruitment and selection of follicles destined to ovulate in the pig. 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Day Symposium. 2 Mention of a trade name or proprietary product does not constitute a guarantee or warranty by the USDA and does not imply approval to the exclusion of others mentioned. Copyright 2005 Journal of Animal Science

Horn, G. W.; Beck, P. A.; Andrae, J. G.; Paisley, S. I.

doi: 10.2527/2005.8313_supple69xpmid: N/A

Supplementation of cattle grazing wheat pasture is of interest to 1) provide a more balanced nutrient supply and feed additives such as ionophores or bloat preventive compounds, 2) substitute supplement for forage where it is desirable to increase stocking rate in relation to grazing management and/or marketing decisions, and 3) substitute supplement for forage under conditions of low forage standing crops. Two different strategies for providing energy supplements to growing cattle on wheat pasture are presented. One was to develop a “small package” (i.e., target intake of 0.91 to 1.36 kg/d on an as-fed basis), self-limited monensin-containing energy supplement to provide additional degradable OM relative to rumen degradable N and increase nonammonia N supply per unit of ME. The supplement very consistently increased ADG by approximately 0.22 kg and increased profit by $15 to 31/steer depending on supplement cost and profit potential of the cattle. The sorghum grain-based supplement contained (as-fed basis) 4% fine mixing salt, 165 mg/kg of monensin, and 0.75% magnesium oxide. Monensin limited intake, but MgO at concentrations up to 1.75% did not limit intake. Modification of the formula for every-other-day hand-feeding resulted in similar improvements in ADG as achieved with the self-limited supplement. An additional study using small numbers of ruminally cannulated steers in a completely randomized design compared the effects of monensin or lasalocid vs. no ionophore on wheat pasture bloat. Monensin decreased (P < 0.05) both the incidence and severity of bloat and was more efficacious than lasalocid for prevention of bloat. A second strategy was to feed two types of energy supplements (i.e., high-starch, corn-based supplement vs. high-fiber by-product feed-based supplement) at a level of 0.75% of BW. Over the 3-yr study, mean daily supplement consumption was 0.65% of BW. This energy supplementation program increased ADG by 0.15 kg and allowed stocking rate to be increased by one-third. Type of supplement did not influence ADG, supplement conversion, or the substitution ratio of supplement for forage. Supplement conversion was approximately 5 kg of as-fed supplement•kg of increased gain−1•ha−1 and was substantially less than conversions of 9 to 10 that have traditionally been used in evaluating the economics of energy supplementation programs for wheat pasture stocker cattle.

Hogberg, M. G.;Fales, S. L.;Kirschenmann, F. L.;Honeyman, M. S.;Miranowski, J. A.;Lasley, P.

doi: 10.2527/2005.8313_supplE13xpmid: N/A

Abstract Animal agriculture is closely interrelated to both the natural environment and human systems, including rural communities. Accordingly, changes in animal agriculture can have wide-ranging consequences across many areas. During the past 50 yr, there has been tremendous change in animal agriculture, involving an increase in the size of production units, greater reliance on technology, a corresponding decrease in human labor, increased confinement of animals, and a general trend toward monoculture or specialized production systems. At least in part, these changes were brought about as a consequence of animal science research in nutrition, breeding, reproduction, growth, and so on. A long-term goal for animal scientists has been to increase the biological efficiency of animal-based food production, and the success in reaching this goal has been remarkable, with the time to market, growth rates, milk and egg production, etc., per animal increasing two- to threefold in some cases during the last 50 yr. The increase in the efficiency of animal agriculture has brought about a parallel decrease in food prices. Nonetheless, whereas animal science in one sense has been very successful, new questions or issues have emerged. The scale of animal systems today sometimes concentrates large numbers of animals into smaller areas that cannot handle the resultant animal manure. Stream and ground water pollution is increasingly a concern in some regions. Odor is a nuisance problem that increasingly places neighbors and urban growth in conflict with confinement animal systems. Possibly one of the biggest issues can be stated in terms of sustainability: Can all current food animal production systems continue as they currently exist? Additionally, the decrease in the number of producers has affected rural communities, and in some cases has brought about the demise of small towns. Animal scientists typically contend that they serve the interests of producers and strive to promote practices that are environmentally sound. Bringing about a discussion among animal scientists as to whether these goals are always met, or could be better met, is important if both the industry and our rural communities are to survive and thrive. Introduction The face of animal agriculture has changed dramatically during the past 50 yr. Dating back to the development of mixed farming systems during the Middle Ages in Europe, humans, plants, and animals were all integrated to achieve sustainability (Grigg, 1974). Plants produced food for humans and animals, animals produced food and fiber for humans, and nutrients flowed from humans and animals back to plants to produce more food for humans and animals. As society urbanized, plants still produced food for humans and animals, animals provided food for humans, but only animals recycled nutrients back to the plants. More recently, because of the industrialization and specialization of agriculture, the cycle of plants providing food for animals and humans, animals providing food for humans, and nutrients recycling from humans and animals that replenished the soil decreased as agriculturists came to prefer the convenience, cost, and consistency of nutrients from commercial fertilizer. In many cases, animal production occurred as separate specialized operations, and some facilities were far away from plant production facilities. This change has had a major effect on the structure of animal agriculture, which has focused on improving the efficiency and productivity. Economic viability and profitability have been the primary driving forces that define the current structure. More recently, the values of society have demanded a more sustainable environmental system from animal agriculture. The effect of animal agriculture on rural communities also is being recognized as an important consideration (Honeyman, 1996). In this article, we examine the relationships between animal agriculture, the environment, and rural communities and offer thoughts on how to integrate societal values for the future. We will begin with a discussion of ethics, addressing what is generally considered to be “good” or “bad” with regard to food production systems. We will then discuss current animal agriculture, why it is the way it is, and what effects it has on the environment. Finally, we examine the effects of our systems on rural communities, taking into account both economic and social consequences. Ethics Ethics is the study of principles that define behavior as right, good, and proper (Josephson, 2002). Since Socrates, the study of moral philosophy has helped humans clarify what is the right thing to do in certain situations. Moral philosophy addresses the ageless question of “how we ought to live and why” (Rachels, 2003). Ethics involves the changing values of society. It is an agreed upon understanding about what is normal. It is important to understand that what is considered “normal” will vary with culture. Why is ethics being applied to food and agriculture? The answer is that ethical behavior has always been an important component of sustainable communities (Anthony, 2004). Traditionally, farmers were accountable to their communities and the land on which they lived. If they failed to produce food, or if their practices resulted in harm to the environment or community, they were held accountable. In today's industrial agriculture, the ethics of accountability is often eclipsed by economics. Meanwhile, we seem to be facing a much more complex set of ecological circumstances (Kirschenmann, 2004). Animal agriculture, like other sectors of the economy, is organized according to the principles of economics. Asset managers and consumers, who are separated from food production, make decisions about farming practices, leaving some to argue that the restructuring of the food system is challenging the assumed norms of behavior. The reaction to industrialized animal agriculture is that it no longer sustains good relationships, no longer recognizes equitable balance of interests, and no longer promotes trust (Anthony, 2004). Specifically, complaints include the magnitude, intensification, cheap food mentality, and the relocation of the decision-making power of industrial animal agriculture, as well as consumer ignorance and apathy relative to what has happened. What happens when there is no adherence to a code of ethics? As an erosion of ethics occurs, people begin to cut corners (Lasley, 2003). Rationale and justifications often include “everyone else is doing it.” As the application of ethical principles erodes, this results in calls for greater regulation because the trust has been violated. Because there is a lack of trust that people will do what is ethically right, rules, regulations, and laws are sought to force people to “do the right thing” or avoid behavior that may endanger others. With diminished respect, trust, and cooperation, come calls for regulations to monitor behaviors. Those who grew up in the rural, midwestern United States quickly recognize that this is definitely a change in the norm and values of rural communities and farms. The long-term sustainability of agriculture and the ability to feed the nation's people is a value held throughout rural America. Attaining this goal requires that animal agriculture must not only be efficient and profitable, but it also must contribute to maintaining the rural community economy, as well as sustain or improve environmental quality. If society perceives that animal agriculture is degrading the environment or leading to the demise of rural communities, then animal agriculture will lose the support and trust of society, resulting in more regulations that attempt to monitor and control the behavior of the industry. Animal Agriculture and the Environment Animal agriculture, if properly managed, can have a positive, beneficial effect on the environment. Conversely, if mismanaged, it can have a negative effect on the environment. In fact, livestock production and the subsequent application of manure can counteract two major negative effects of crop production: decreasing soil fertility and soil erosion (Baker et al., 1990). Theoretically, maintaining or improving water quality is achievable, with proper agronomic and animal production practices. For animal agriculture, this can be achieved by recycling nutrients back to crop production through proper application of manure to cropland. Minimizing nutrient loss in the system and using phosphorus as a basis for applying manure to cropland will maintain or improve water quality in most situations. Viewing manure as a valuable resource rather than as a waste product to be disposed of is a critical first step in reestablishing the nutrient recycling process. Integrated animal/crop production systems have a financial advantage over specialized operations when crop subsidy payments are not considered (Borts et al., 2004; Flora et al., 2004). The study of Borts et al. (2004) used stochastic budget analysis to compare a diversified swine-grain farm with a cash-grain farm, and showed that the diversified swine-grain farm greatly decreased fertilizer costs by using manure, had shared implement costs, and had more stable grain pricing/costs and thereby less risk. Furthermore, Flora et al. (2004) showed that ruminant production, based on perennial forages, could enhance rather than detract from water quality and decrease nutrient losses from farms. The USDA farm subsidy payments often encourage row cropping on land that is better suited for perennial forage production. Using crop phosphorus needs as the basis for manure application to land will require significantly more land and will be more expensive in areas with limited cropland (Ribaudo et al., 2003). Many specialized, large livestock farms often lack adequate land base for appropriate manure application. Their costs of production may be higher due to the need to haul manure longer distances or the cost of equipment for manure processing facilities. Costs will be lower in the Corn Belt, where cropland is more plentiful, and higher in the mid-Atlantic and South, where cropland may be limited. In the Corn Belt, 70% of the land is in row crop production compared with 20% in the mid-Atlantic region (Ribaudo, 2003). With larger production systems, and in some areas where nutrients produced in the manure far exceed crop needs, land application alone may be insufficient to handle all generated manure economically. Changing the structure of livestock production or adopting alternative technologies to handle manure may be necessary to maintain water and/or air quality standards. The more challenging environmental standard to meet is air quality because it is difficult to quantify and control. With the emergence of larger livestock operations, there has been an increasing concentration and intensity of odors. There also is a change in the unwillingness of neighbors to accept livestock odors. In a study of rural families, the percentage of people finding odors a nuisance in 1 to 2 d went from 12% to 20% in 3 yr (1992 to 1995; Jolly and Kliebenstein, 1995). The trend is for rural residents to have less tolerance and be more demanding for quality of life. There also is a changing perception of who “owns” or has property rights to clean air, producers or society, which has led some to suggest that payment be made to rural residents who are inconvenienced by odors or who suffer loss of property values due to the amount of odors generated. This seems more prevalent for livestock operators who are new to the community than to locally owned and operated facilities, again relating to the trust factor. Long-term livestock producers with established reputations for protecting the environment and respecting their neighbors are more trusted than newcomers that have often been oblivious to local norms or customs. As livestock operations increase in size, different technologies will be needed to maintain air quality standards. One set of statistics explains why we see more discontent with odors from livestock operations among farmers. According to the U.S. Census of Agriculture (NASS, 2002), the percentage of farms with livestock has dropped significantly in the past 50 yr: poultry farms have dropped from 78 to 4.6%, dairy from 68 to 4.3%, and swine from 56 to 3.7%. The most notable drop in the past 10 yr is the percentage of swine farms, which has dropped from 9.9 to 3.7%, whereas poultry farms have remained constant. The percentage of farms with beef has remained constant at approximately 41% for the past 30 yr, which probably is a reflection of the extensive nature of beef production systems. Fewer livestock farms (NASS, 2002), in ever larger units, coupled with more farmers and rural residents without livestock, presents significant challenges on how to ensure the quality of life of both farm and rural nonfarm neighbors. As the size of livestock operations has grown, so has the environmental risk. Manure, once viewed as a resource to be conserved and used on cropland, is now considered by many a waste disposal problem. As a result, there is a tendency for overapplication of nutrients to the land, volatilization of ammonia and hydrogen sulfide gases, and excessively large lagoons, all which have compromised water supplies and air quality. In the future, we will need to apply technologies that are consistent with the values of society. We also need to direct research efforts to develop systems of animal production that value and preserve natural resources. One solution is to develop performance standards or expected outcomes for environmental quality for the livestock industry. Livestock producers would then know what the water and air quality standards are and would adjust their management and use of technologies to meet those standards. When technologies and management practices are properly used, the effects of animal agriculture on the environment should be neutral. Small livestock facilities that are mismanaged can have a larger negative impact on the environment than properly managed larger facilities. Although there are suspicions that size is the culprit, it seems that the level of management and attention to detail may be more critical than the number of livestock at a site. Animal Agriculture and Rural Communities Animal agriculture can have a significant effect on rural communities and their vitality. Animal production systems need to fit within the values of rural communities if they are to be accepted. Rural Iowans and farmers (Korsching et al., 2003) indicated that they favor the following: 1) increasing biotechnology research for products from agriculture and uses of biotechnology in agriculture production; 2) increasing local processing of grains and livestock; 3) improving rural infrastructure, such as road, schools, housing; 4) increasing the state emphasis on agriculture exports; 5) diversifying agriculture production to specialty crops; 6) focusing on retention and expansion of existing industries; 7) tax incentives to retain the youth in the state; and 8) focus on economic development by universities. They also were in general agreement on what they did not favor. These items were 1) increasing the population to match growth of surrounding states; 2) developing more racetracks and casinos; and 3) gambling opportunities for tourism. Rural residents and farmers also were in general agreement on what they viewed as desirable and undesirable development activity. Farmers markets and windmill farms ranked high as desirable development activity. Confinement hog lots ranked low, even below prisons, solid waste landfills, slaughter plants, and sewage treatment plants when considering what people were willing to accept (Korsching et al., 2003). Obviously, the image of confinement swine operations is quite low and may reflect the need to address the issue of trust and how new facilities will be designed and managed in a way that is both socially and ecologically acceptable. It is obvious that the quality of life aspect is important and probably surpasses the economic development advantages if community members perceive that animal production development will degrade their environment and quality of life. The economic development aspects of animal agriculture alone are not sufficient to be construed as a socially acceptable development in the rural communities. Economically, livestock add greatly to the economic growth and vitality of the community. Livestock production systems add jobs on the farm, at local businesses, and in the community, as well as helping to keep the population stable, which supports local social institutions such as churches and schools. A recent study showed that with a 10% higher share of county income from agricultural production (crop production), there was a 7.7% decrease in county income growth or a $100 per capita lower income (Hayes et al., 2004). Similarly, a 10% growth in livestock receipts resulted in a 0.5% increase in county income or a $77 higher per capita income. Counties with 10% more outdoor recreation amenities in 1990 experienced a $180 higher per capita income in 2001. It is not surprising that counties with recreational facilities have higher incomes, and it is those counties where extra care must be exercised when expanding livestock production. Livestock production systems can have a positive effect on the economic vitality of rural communities, but where major recreational opportunities exist, the livestock systems must be designed and managed in a manner that is compatible with people enjoying recreational activities and their quality of life. Further, the economic impact of a 3,400-sow, farrow-to-finish unit can be significant because it would employ 21 new workers, provide 19 additional indirect jobs, and generate nearly $1 million in new income if locally owned and financed. Moreover, a unit of this size implies 10 additional school age children, provides additional property tax revenues of $27,000, and increases state income tax revenues of $65,000 (Otto et al., 1998). These studies indicate that properly structured and managed livestock systems can help a rural community to develop and grow. Livestock production can be a source of jobs to retain young people in the community. Additional jobs help to stabilize the local population by contributing to the maintenance of school systems and local businesses and other social institutions. The challenge is to develop systems of livestock production that keep money in the local community, create meaningful, well-paid employment opportunities, and develop the trust of the community that the operations will be managed in an environmentally acceptable manner. Implications For animal scientists, these findings have several implications. The decision-making process on farms is becoming more complex. No longer can producers make decision based on production efficiency and profitability alone. Instead, their decisions need to include the impact on the environment and how they contribute to the local community. Animal scientists also need to consider the environmental and community effects of research and management programs. It also is important that animal scientists and livestock producers develop production systems that integrate and respect local community values and consider environmental impacts. There is a need to evaluate, refine, and demonstrate these technologies and create business systems that minimize external costs and effects on society. Literature Cited Anthony, R. 2004. Ethics and animal agriculture-two overviews. Presentation at the Sustainable Agriculture Colloquium, spring semester 2004.  Dept. of Philosophy and Religious Studies. Iowa State Univ., Ames. Baker, F. H., F. E. Busby, N. S. Raun, and J. A. Yazman 1990. The relationships and roles of animals in sustainable agriculture on sustainable farms. Prof. Anim Sci.  6: 36– 49. Borts, L., G. May, and J. D. Lawrence 2004. Diversified versus specialized swine and grain operations. ASL-R1959. ISU Anim. Ind. Rep. Dept. of Anim. Sci.,  Iowa State University, Ames. Flora, C., J. R. Black, T. J. Dalton, R. Kershegan, M. Liebman, S. N. Smith, S. S. Sapp, and G. K. White 2004. Reintegrating crop and livestock enterprises in three northern states. Preliminary Report on USDA-IFAFS Project 2001-52101-11308.  Iowa State Univ., Ames. Grigg, D. B. 1974. The Agricultural System of the World: An Evolutionary Approach.  Cambridge Univ. Press, Cambridge, U.K. Google Scholar CrossRef Search ADS   Hayes, D., J. Miranowski, B. Babcock, D. Otto, and D. Monchuk 2004. Improving economic vitality in rural Iowa: A data-based approach. Committee of 82 Report.  Dept. of Econ., Iowa State Univ., Ames. Honeyman, M. S. 1996. Sustainability issues of U.S. swine production. J. Anim. Sci.  74: 1410– 1217. Google Scholar CrossRef Search ADS PubMed  Jolly, R., and J. Kliebenstein 1995. Economic issues in livestock odor reduction. Pages 163– 167 in Proc. New Knowledge in Livest. Odor Solutions Int. Livest.  Conf. Iowa State Univ., Ames. Josephson, M. 2002. Making Ethical Decisions.  Josephson Inst. of Ethics, Marina del Ray, CA. Kirschenmann, F. 2004. Ecological mortality: A new ethic for agriculture. In Agroecosystems Analysis. Agronomy Monograph No. 43. Am. Soc. Agron., Crop Sci. Soc. Am., Soil Sci. Soc. Am.,  Madison, WI. Korsching, P., P. Lasley, and D. Roelfs 2004. Rural Iowa Life Survey 2003 Summary Report. Iowa State Univ. Ext. Bull. PM 1960.  Iowa State Univ., Ames. Lasley, P. 2003. Strengthening ethics in agriculture. Presentation to the Iowa Master Farmers.  Dept. of Sociology, Iowa State Univ., Ames. NASS 2002. Census of Agriculture.  Natl. Agric. Stat. Serv., USDA, Washington, DC. Otto, D., P. Orazem, and W. Huffman 1998. Community and economic impacts of the Iowa hog industry. Iowa Pork Industry-Dollars and Scents. PM 1746.  Iowa State Univ., Ames. Rachels, J. 2003. The Elements of Moral Philosophy.  McGraw-Hill Co., Inc., New York, NY. Ribaudo, M. 2003. Managing manure: New Clean Water Act regulations create imperative for livestock producers. Amber Waves, February 2003. Econ. Res. Serv.,  USDA, Washington, DC. Ribaudo, M., N. Collehon, M. Aillery, J. Kaplan, R. Johansson, J. Agapoff, L. Christensen, V. Breneman, and M. Peters 2003. Manure management for water quality: Cost to animal feeding operations of applying manure nutrients to land. Rep. 842, Econ. Res. Serv.  USDA, Washington, DC. Footnotes 1 Presented at the ASAS Symposium: Ethics and the Cost of Food, St. Louis, MO, July 27, 2004. Copyright 2005 Journal of Animal Science

McMillin, K. W.;Brock, A. P.

doi: 10.2527/2005.8313_supplE57xpmid: N/A

Abstract This review discusses adding value to goat meat, with an emphasis on the properties of goat meat and processed products. Goat meat value may be increased through production practices or meat processing. Decreasing the market channel steps or distribution costs and marketing animals in uniform or consistent groups will generally increase live animal value. Processing of meat into more palatable and usable forms or providing meat at times of higher purchaser demand will usually increase the price of the meat. Age, breed, and diet influence tenderness, juiciness, and flavor, with higher fat in carcasses and cuts from goats fed concentrate diets. The meat from kid and yearling goats of low conformation could be distinguished by goat meat consumers from the meat of goats with medium and high conformation. Ethnic groups that purchase goat meat have high levels of population growth and are increasing their buying power. Higher income populations desire value-added food products, which have been changed in form, function, or grouping to increase their economic value and/or appeal; however, lower income groups have a supply of imported frozen goat meat at a price lower than domestic sources. Food service operations purchase uniform cuts and sizes of meat, which are provided through USDA Institutional Meat Purchase Specification descriptions for goat meat. Goat meat also may be processed with unit operations similar to those for other meat species. Tenderness of domestic goat meat was improved with postmortem goat carcass aging, electrical stimulation of goat carcasses, and blade tenderization of goat cuts. The addition of α-tocopherol increased the oxidative stability of goat meat patties, whereas the addition of oat trim or oat bran decreased fat and shear force. Smoked and fermented goat meat sausages were acceptable to consumers, but they are more expensive per unit weight than sausages from other species. Emulsification capacity of goat meat proteins is high, and the palatability of frankfurters was increased with the use of mechanically separated goat mince. Goat meat was distinguishable from other species in plain and seasoned meat loaves, chili, curries, and patties. Specific organic acids are associated with goat meat flavor, and oxidized flavors develop more rapidly in cooked goat meat than in meat from other species. More convenient product forms and the availability of goat meat would increase the value and penetration of goat meat in ethnic and nontraditional consumer markets. Introduction Goat farming is practiced worldwide, with goat products having a favorable image (Morand-Fehr et al., 2004). The number of goats has increased globally, even in countries with high and intermediate incomes (Morand-Fehr et al., 2004), despite major changes in agriculture due to industrial mergers, globalization, and technological advances in developed countries (Boehlje and Sonka, 1998; Cheeke, 2004). Competitive advantages sustain production and marketing within the constraints of financial and strategic risks. Value chains that lower costs, manage risk, and respond to consumer demands are developing (Boehlje et al., 1999). Consumer food trends include convenience requirements, more meat, innovative dairy products, and growth in ethnic foods and one-dish meals, which include sandwiches, bowls, or cups as the entrée (Sloan, 2003). Convenience may mean less time for shopping, speed or ease of preparation, speed or ease of consumption, ready-to-eat or no preparation, or portability. Consumers often are willing to pay higher prices for convenient versions of their favorite products (IRI, 2002). Value-added products are a means to provide convenience and economic profitability. Value-added products have been changed in form, function, or grouping to increase their economic value and/or consumption appeal (USDA, 2004). Value may be added to final products by decreasing costs or improving relative value (price received) of the final product. Costs may be decreased by using fewer market channel steps, lowering production or distribution costs, and by using uniform or consistent groups for inventory and display control. Relative value or price received is increased through products that are more palatable, usable, or available in a different form or time after sorting or processing. The relative value, and thus the amount of value that has been added or is available to the producer of the commodity or product, is ultimately determined through amounts and prices of purchases by consumers. The differences in attitudes and behaviors of various ethnic groups are important to businesses in terms of the goods and services that are offered (Gardyn and Fetto, 2003). Ethnic groups may be defined as having a common and distinctive racial, national, religious, linguistic, or cultural heritage. The distribution of racial and ethnic diversity in the United States is uneven because of diverging migration patterns of immigrants and domestic groups (Frey, 2004). Some states, such as Texas and Florida, have attracted both immigrants and domestic migrants (Frey, 2002). A challenge to businesses will be the development of products that appeal to many demographic segments, because the Asian and Hispanic populations will almost double in the next 25 yr (Wellner, 2003). The demand for goat meat in the United States has been centered in areas with ethnic populations that use goat meat as a traditional staple (Hansen, 2003), with consumers from many different ethnic groups, including Muslim, Latino, Asian, Afro-American, Haitian, and Eastern European, eating goat meat (Pinkerton, 2002). Some ethnic markets in Florida use a higher proportion of imported frozen goat meat than other geographical areas, with price being the primary determinant of demand and consumption (Nuti et al., 2003b). Increased urban demographic growth has increased the demand for goat meat even though low innovation has contributed to the difficulty in preparing and cooking goat meat by urban peoples (Dubeuf et al., 2004). Opportunities exist for goat meat because of its ecological image, dietetic and health qualities, and association with religious holidays, along with the tendency of consumers toward natural foods (Dubeuf et al., 2004). Trends toward healthier diets could increase the demand for value-added products from nontraditional meat sources, such as goat meat, to supply products with decreased fat, lower cholesterol, and less sodium (Dawkins et al., 1999). The potential for ethnic, value-added, and convenient items is very high (Sloan, 2005), presenting justification for adding value to goat meat and goat meat products to stimulate growth and profit-ability of meat goat production. Influences of Production Practices on Addition of Value to Goat Products The value of goat meat in the United States is affected by the seasonal availability of live goats, with the price per weight of goats highest in late winter and early spring (Figure 1; Pinkerton and McMillin, 2005). The highest price spikes also coincide with religious and ethnic holiday dates (Pinkerton, 2002), whereas the lowest prices are in the summer when demand is least and supply is greatest (Farris, 2003). Seasonal breeding and forage conditions of domestic goat production make it difficult to adjust birth, weaning, and growth cycles to match periods of high consumer demand (Nuti et al., 2000b). Size uniformity requirements are reflected in the live goat markets, with kid goats weighing 18 to 36 kg bringing higher relative prices per unit of weight than those weighing more than 36 kg (Farris, 2004). Goats weighing 36 kg or over may be discounted in live animal markets because of the undesirable size and product traits of the resulting goat meat cuts. Increasing the live slaughter weight from 16 to 28 kg increased dressing percent and carcass fat thickness with corresponding increases in shear force values and lower overall sensory acceptability scores (Dhanda et al., 2003a). Those data only partially agreed with an earlier report that increased age and weight at slaughter increased carcass dressing percents and proportions of lean to fat and bone (Ruvuna et al., 1992). Slaughter at 25 kg decreased water binding and hue and increased a* value (redness), chroma, shear force, and fiber type areas in goat meat compared with slaughter at 6 kg. In the same study, fat, collagen solubility, and Type I fiber percent were not changed with slaughter weight (Argüello et al., 2000). Additionally, if increased live weights at marketing were achieved with minimal input costs, then the profit margin of producers potentially could increase through increased weight gains and total income per unit of input. Production costs are another factor influencing the relative value of goats. Harvesting of feral goats in Australia results in frozen goat meat delivery into the United States at a lower cost per unit of weight than for goat meat from domestic sources in the same geographic area (Nuti et al., 2003b). Figure 1. View largeDownload slide Average monthly prices and goats sold through Producers Auction, San Angelo, TX, 2002 through 2004 (adapted from Pinkerton and McMillin, 2005). Jan, Mar, Jul, Sep, and Nov = January, March, July, September, and November, respectively. 02, 03, and 04 = 2002, 2003, and 2004, respectively. Figure 1. View largeDownload slide Average monthly prices and goats sold through Producers Auction, San Angelo, TX, 2002 through 2004 (adapted from Pinkerton and McMillin, 2005). Jan, Mar, Jul, Sep, and Nov = January, March, July, September, and November, respectively. 02, 03, and 04 = 2002, 2003, and 2004, respectively. Age and Sex As with most livestock species, the age and sex of the goat influence meat properties and relative value. Young goats generally produce more tender meat than older goats (Kirton, 1970; Gaili et al., 1972; Riley et al., 1989), but conformation and breed may influence the effects of age on meat properties (Smith et al., 1978). The leg slices in meat from yearling goats and kid goats with low conformation were less tender than leg meat from kid goats having medium or high conformation (Phelps et al., 1999). Loin chops and leg roasts from young Angora goats were more tender than from year-ling Angora goats, but meat from 6-mo-old Spanish goats was more tender than from 4-mo-old or yearling Spanish goats (Smith et al., 1978). The LM from dairy goats 6 to 12 mo of age was more tender than those from dairy goats 24 to 30 mo old (Kannan et al., 2003). Organoleptic properties of tenderness, appearance, aroma, flavor, juiciness, and overall palatability were decreased with goat age from 175 to 310 d. Meat from goats slaughtered at 175 d of age had a lower number of volatile compounds and intensity as measured by total relative abundance, and was preferred by semi-trained sensory panelists over meat from older animals (Madruga et al., 2000). Smith et al. (1978) had previously reported that flavor was more intense in leg roasts from young vs. yearling Angora goats, but age did not influence the flavor of leg and sirloin chops from Spanish goats or the flavor of loin chops from Angora and Spanish goats. Increased age of goat also was reported to increase drip loss, with the meat from older animals with seven to eight permanent incisors being judged to have lower initial and sustained juiciness than goat meat from younger animals with no permanent incisors (Schönfeldt et al., 1993b). Fatty acids in meat from goats raised on forage changed with goat age. Octadecanoic acid, oleic acid, and cholesterol increased, whereas linolenic acid decreased in the lean composite mixtures from carcasses of goats with increased slaughter age from 4 to 6 mo to 8 to 10 mo (Beserra et al., 2004). However, Dhanda et al. (2003b) reported that oleic and linoleic acids increased in intermuscular adipose tissue of male goats at 254 d of age compared with younger counterparts at 93 d of age. Sex class also influences carcass composition and meat properties of goats, with fat tissue being the most affected (Mahgoub et al., 2004). Intact males were reported to have higher lean-to-fat-to-bone percents (75:10:15) than castrated males (68:18:14; Ruvuna et al., 1992). These data substantiated the findings of Bayraktaroglu et al. (1988) that castrated males had more mesenteric, kidney, and channel fat and lower weights of carcass cuts than intact males. Carcasses from intact males had higher contents of muscle and lower contents of fat than carcasses from females (Colomer-Rocher et al., 1992), whereas carcasses of castrated male kid goats had higher percentages of lean and lower amounts of carcass and omental fat than carcasses from female kid goats (Hogg et al., 1992). Those findings were contradicted by Wilson (1960), who reported that female East African dwarf kid goats had higher fat and less bone in the body than male goats, with greater differences with increased age. Johnson et al. (1995b) also reported that carcasses of female kid goats had less bone, more fat, and higher percentages of fat-free lean percents than did those of intact males, which had less bone, less fat, and higher amounts of fat-free lean than carcasses of castrated males. There were no differences in moisture, fat, or protein contents of uncooked composite goat samples from intact male, female, or castrated kid goats of 21 to 28 kg slaughter weight (Johnson et al., 1995b). Mahgoub et al. (2004, 2005) reported that weight at slaughter influenced composition, with wethers having more total carcass and total body fat than intact males or females at an 11-kg slaughter weight, whereas female does had more total body and carcass fat than wethers, which had more fat than intact males, at 18- and 28-kg slaughter weights. Goats with a lighter carcass weight of 16 kg were used in the Hogg et al. (1992) study, whereas a range of carcass weights from 2 to 52 kg on 37 male and female Saanen goats was reported in the Colomer-Rocher et al. (1992) study, which may explain some of the differences in results. At 47 d of age, weight at slaughter was lower for female kid goats than for male goats, but dressing percents and tissue composition were not different. Twins had higher gains than singles to achieve the same slaughter weight, dressing percents, and tissue composition as single goats (Todaro et al., 2004). The shear force values of longissimus, biceps femoris, semimembranosus, and semitendinosus muscles from female carcasses were lower than those from castrated male carcasses, which had lower shear force values than those muscles from intact male carcasses (Johnson et al., 1995b). Madruga et al. (2000) reported no differences in sensory attributes of meat from intact and castrated goats at differing slaughter ages. Composite broiled leg slices from intact males had higher unsaturated fatty acid content than did broiled slices from female or castrated goats (Johnson et al., 1995a). However, Santos-Filho et al. (2005) reported no differences in unsaturated fatty acid composition in meat from intact or castrated male goats at 20 kg BW, whereas cholesterol and total saturated fatty acids were increased in meat from castrated males. Breed Goat breed will often influence carcass composition and characteristics, with resulting differences in carcass and meat value, even though three breeds of goats from India were reported to have the same HCW and muscling (Nagpal et al., 1995). Dressing percents (yield of carcass) were higher in young intact males of Spanish vs. Angora breeding, but tenderness was similar in meat from goats of the two breeds at the same age (Riley et al., 1989). Boer × Spanish goats had carcasses with higher conformation scores and larger leg circumference than carcasses from Spanish goats, but lean, bone, and fat were similar in the carcass and wholesale cuts within diet group (Table 1; Oman et al., 1999). The juiciness of goat meat was reported to be the same in loin chops and leg roasts from Angora and Spanish goats of the same age (Smith et al., 1978). This finding was contradicted by Schönfeldt et al. (1993a, b), who reported that meat from Angora goats was more tender and juicy and had lower shear resistance and lower collagen content than meat from Boer goats. Higher cooking losses and higher unsaturated fatty acids were reported in meat patties from Spanish than Angora goats (Rhee et al., 1997). There was no influence of breed (Boer × Spanish, Spanish, Spanish × Angora, Angora) on retail shelf life (color, appearance, odor) of goat meat in air-permeable packaging (Oman et al., 2000). Table 1. Selected characteristics of carcasses from Boer × Spanish and Spanish goats from feedlot or range regimensa Item  Boer × Spanish Feedlot  Boer × Spanish Range  Spanish Feedlot  Spanish Range  SEM  Live weight, kg  38.17c  20.51e  33.52d  18.42e  1.21  Hot carcass weight, kg  21.72c  10.00e  19.24d  8.75e  0.60  Dressing percent (calculated)  56.90  48.76  57.40  47.50  NA  Adjusted fat thickness, cm  0.16c  0.04e  0.11d  0.04e  0.01  Carcass conformation scoreb  11.42c  3.25e  8.33d  1.83e  0.65  Leg circumference, cm  54.87c  44.03e  52.61d  42.60e  0.63  Lean, % of carcass side  57.79c  55.78cd  57.61c  55.28d  0.65  Bone, % of carcass side  26.50d  36.89c  27.58d  36.48c  0.82  Fat, % of carcass side  15.71c  7.34d  13.40c  8.24d  0.81  Lean, % of wholesale leg  62.23c  59.56d  62.52c  59.05d  0.59  Bone, % of wholesale leg  29.54d  35.47c  31.01d  35.90c  0.57  Fat, % of wholesale leg  8.23c  4.97e  6.74d  5.05e  0.51  Item  Boer × Spanish Feedlot  Boer × Spanish Range  Spanish Feedlot  Spanish Range  SEM  Live weight, kg  38.17c  20.51e  33.52d  18.42e  1.21  Hot carcass weight, kg  21.72c  10.00e  19.24d  8.75e  0.60  Dressing percent (calculated)  56.90  48.76  57.40  47.50  NA  Adjusted fat thickness, cm  0.16c  0.04e  0.11d  0.04e  0.01  Carcass conformation scoreb  11.42c  3.25e  8.33d  1.83e  0.65  Leg circumference, cm  54.87c  44.03e  52.61d  42.60e  0.63  Lean, % of carcass side  57.79c  55.78cd  57.61c  55.28d  0.65  Bone, % of carcass side  26.50d  36.89c  27.58d  36.48c  0.82  Fat, % of carcass side  15.71c  7.34d  13.40c  8.24d  0.81  Lean, % of wholesale leg  62.23c  59.56d  62.52c  59.05d  0.59  Bone, % of wholesale leg  29.54d  35.47c  31.01d  35.90c  0.57  Fat, % of wholesale leg  8.23c  4.97e  6.74d  5.05e  0.51  a Adapted from Oman et al. (1999). b 15-point descriptive scale, 1.0 = very angular, narrow, thin; 15.0 = extremely thick, bulging. c,d,e Means within a row without a common superscript letter differ, P < 0.05. View Large Table 1. Selected characteristics of carcasses from Boer × Spanish and Spanish goats from feedlot or range regimensa Item  Boer × Spanish Feedlot  Boer × Spanish Range  Spanish Feedlot  Spanish Range  SEM  Live weight, kg  38.17c  20.51e  33.52d  18.42e  1.21  Hot carcass weight, kg  21.72c  10.00e  19.24d  8.75e  0.60  Dressing percent (calculated)  56.90  48.76  57.40  47.50  NA  Adjusted fat thickness, cm  0.16c  0.04e  0.11d  0.04e  0.01  Carcass conformation scoreb  11.42c  3.25e  8.33d  1.83e  0.65  Leg circumference, cm  54.87c  44.03e  52.61d  42.60e  0.63  Lean, % of carcass side  57.79c  55.78cd  57.61c  55.28d  0.65  Bone, % of carcass side  26.50d  36.89c  27.58d  36.48c  0.82  Fat, % of carcass side  15.71c  7.34d  13.40c  8.24d  0.81  Lean, % of wholesale leg  62.23c  59.56d  62.52c  59.05d  0.59  Bone, % of wholesale leg  29.54d  35.47c  31.01d  35.90c  0.57  Fat, % of wholesale leg  8.23c  4.97e  6.74d  5.05e  0.51  Item  Boer × Spanish Feedlot  Boer × Spanish Range  Spanish Feedlot  Spanish Range  SEM  Live weight, kg  38.17c  20.51e  33.52d  18.42e  1.21  Hot carcass weight, kg  21.72c  10.00e  19.24d  8.75e  0.60  Dressing percent (calculated)  56.90  48.76  57.40  47.50  NA  Adjusted fat thickness, cm  0.16c  0.04e  0.11d  0.04e  0.01  Carcass conformation scoreb  11.42c  3.25e  8.33d  1.83e  0.65  Leg circumference, cm  54.87c  44.03e  52.61d  42.60e  0.63  Lean, % of carcass side  57.79c  55.78cd  57.61c  55.28d  0.65  Bone, % of carcass side  26.50d  36.89c  27.58d  36.48c  0.82  Fat, % of carcass side  15.71c  7.34d  13.40c  8.24d  0.81  Lean, % of wholesale leg  62.23c  59.56d  62.52c  59.05d  0.59  Bone, % of wholesale leg  29.54d  35.47c  31.01d  35.90c  0.57  Fat, % of wholesale leg  8.23c  4.97e  6.74d  5.05e  0.51  a Adapted from Oman et al. (1999). b 15-point descriptive scale, 1.0 = very angular, narrow, thin; 15.0 = extremely thick, bulging. c,d,e Means within a row without a common superscript letter differ, P < 0.05. View Large Meat from Anglo-Nubian goats was more acceptable with less goat flavor than meat from Thai native goats (Intarapichet et al., 1994). Anglo-Nubian kid goats had heavier carcasses with more muscle and less fat while Boer × Saanen kid goats had carcasses with more fat than carcasses of Saanen kid goats (Gibb et al., 1993). The tenderness of back and leg muscles did not differ among goats of Florida native origin or crosses of Florida native with Spanish or Nubian goats (Johnson et al., 1995b). Meat from Cashmere goats was more tender than meat from other breeds, whereas shear force and sensory juiciness were the same in meat from Boer, Cashmere, and Boer × Cashmere goats (Swan et al., 1998). The dressing percent, muscling, shear force, and sensory determinations of tenderness, flavor, juiciness, and overall acceptability were not different in goats of five different genotypes (Boer × Angora, Boer × Saanen, feral × feral, Saanen × Angora, Saanen × feral) at the same live weight (Dhanda et al., 1999a,b). In other studies, however, dressing percent, fat thickness at the 12th-/13th-rib and rump areas, cooking loss, shear force values, and sensory scores for tenderness, juiciness, and overall acceptability were different among male goats of these genotypes (Dhanda et al., 2003a). Although there were no differences in percentages of the primal cuts with genotype, percentages of muscle in the shoulder and leg were higher and the ratio of unsaturated to saturated fatty acids was lower in intermuscular adipose tissue from goats with feral genotypes (Dhanda et al., 2003b). Johnson (2000) found that 14-to 20-kg capretto carcasses from Boer × Cashmere and Cashmere male kid goats had more s.c. and intermuscular fat than did carcasses from Boer × feral male kid goats. These results were generally reinforced by the findings of Husain et al. (2000) that in 11 genotypes, goats with some feral breeding had higher percentages of muscle and lower percentages of fat in carcasses than goats from established breed genotypes. Imported goat carcasses from Australia, presumably from feral goats, had superior conformation with the same amount of external fat, higher percentages of total primal cuts, and lower percentages of total boneless meat than did carcasses from domestic U.S. goats raised on pasture (Table 2; Nuti et al., 2003c). Table 2. Characteristics of imported and domestic goat meat carcassesa   Source of goats:  Domestic  Domestic  Imported  SEM  Item  Type of feed:  Grain on pasture  Pasture  Pasture (feral)  NA  No. of carcasses    12  12  20  NA  Carcass weight, kg    12.1cd  11.2d  13.8c  0.67  Carcass conformationb    1.19c  2.56d  1.08c  0.30  Fat score (1 = lowest; 3 = highest)    1.59c  1.11cd  1.07d  0.15  Forelegs, % of carcass    15.9d  16.6cd  16.8c  0.24  Boneless foreleg, % of carcass    7.8d  8.5d  9.4c  0.24  Hind leg, % of carcass    28.2c  25.8d  28.1c  0.46  Boneless hind leg, % of carcass    9.8c  9.2c  10.0c  0.26  Total primal cuts, % of carcass    90.2c  86.8e  88.4d  0.47  Total boneless meat, % of carcass    73.2c  68.5c  64.9c  2.54    Source of goats:  Domestic  Domestic  Imported  SEM  Item  Type of feed:  Grain on pasture  Pasture  Pasture (feral)  NA  No. of carcasses    12  12  20  NA  Carcass weight, kg    12.1cd  11.2d  13.8c  0.67  Carcass conformationb    1.19c  2.56d  1.08c  0.30  Fat score (1 = lowest; 3 = highest)    1.59c  1.11cd  1.07d  0.15  Forelegs, % of carcass    15.9d  16.6cd  16.8c  0.24  Boneless foreleg, % of carcass    7.8d  8.5d  9.4c  0.24  Hind leg, % of carcass    28.2c  25.8d  28.1c  0.46  Boneless hind leg, % of carcass    9.8c  9.2c  10.0c  0.26  Total primal cuts, % of carcass    90.2c  86.8e  88.4d  0.47  Total boneless meat, % of carcass    73.2c  68.5c  64.9c  2.54  a Adapted and updated from Nuti et al. (2003c). b Selection score 1 = highest; Selection score 2 = intermediate; Selection score 3 = lowest; range of 0.00 (low) and 0.99 (high) within each selection score. c,d,e Least squares means in a row without a common superscript letter differ, P < 0.05. View Large Table 2. Characteristics of imported and domestic goat meat carcassesa   Source of goats:  Domestic  Domestic  Imported  SEM  Item  Type of feed:  Grain on pasture  Pasture  Pasture (feral)  NA  No. of carcasses    12  12  20  NA  Carcass weight, kg    12.1cd  11.2d  13.8c  0.67  Carcass conformationb    1.19c  2.56d  1.08c  0.30  Fat score (1 = lowest; 3 = highest)    1.59c  1.11cd  1.07d  0.15  Forelegs, % of carcass    15.9d  16.6cd  16.8c  0.24  Boneless foreleg, % of carcass    7.8d  8.5d  9.4c  0.24  Hind leg, % of carcass    28.2c  25.8d  28.1c  0.46  Boneless hind leg, % of carcass    9.8c  9.2c  10.0c  0.26  Total primal cuts, % of carcass    90.2c  86.8e  88.4d  0.47  Total boneless meat, % of carcass    73.2c  68.5c  64.9c  2.54    Source of goats:  Domestic  Domestic  Imported  SEM  Item  Type of feed:  Grain on pasture  Pasture  Pasture (feral)  NA  No. of carcasses    12  12  20  NA  Carcass weight, kg    12.1cd  11.2d  13.8c  0.67  Carcass conformationb    1.19c  2.56d  1.08c  0.30  Fat score (1 = lowest; 3 = highest)    1.59c  1.11cd  1.07d  0.15  Forelegs, % of carcass    15.9d  16.6cd  16.8c  0.24  Boneless foreleg, % of carcass    7.8d  8.5d  9.4c  0.24  Hind leg, % of carcass    28.2c  25.8d  28.1c  0.46  Boneless hind leg, % of carcass    9.8c  9.2c  10.0c  0.26  Total primal cuts, % of carcass    90.2c  86.8e  88.4d  0.47  Total boneless meat, % of carcass    73.2c  68.5c  64.9c  2.54  a Adapted and updated from Nuti et al. (2003c). b Selection score 1 = highest; Selection score 2 = intermediate; Selection score 3 = lowest; range of 0.00 (low) and 0.99 (high) within each selection score. c,d,e Least squares means in a row without a common superscript letter differ, P < 0.05. View Large The unsaturated (1%) and polyunsaturated (0.5%) fatty acids were higher in the LM of indigenous African than from Boer goats, but the patties from indigenous goats were less juicy and greasy than those from Boer goats (Tshabalala et al., 2003). Beserra et al. (2004) found no differences in fatty acid composition in meat from crosses of five breeds. Kadim et al. (2004) reported lower shear force in meat from Batina goats than in goats of Dhofari and Jabal Akdhar breeds, which differed from a previous report that goats of these breeds did not have differences in tenderness of the longissimus, biceps femoris, semitendinosus, or semimembranosus muscles (Kadim et al., 2003). Diet and Stress Goats on a high plane of nutrition had heavier BW with higher levels of body fat than did goats with lower planes of nutrition (Wilson, 1960). Increased concentrate-to-forage ratios increased weight gain, final BW, and G:F of male kid goats, while decreasing feed costs (Haddad, 2005). Feedlot finishing of Boer × Spanish and Spanish goats with 80% concentrate diets ad libitum resulted in increased carcass fat thickness, higher dressing percents, and increased fat percent in primal cuts compared with goats raised on rangeland with no supplemental feeding (Table 1; Oman et al., 1999). The income over cost increased for Boer-cross goats and decreased for Spanish kid goats finished to slaughter weight on 0.23 and 0.46 kg of corn•goat−1•d−1 compared with pasture-finishing with no supplemental corn (Nuti et al., 2000a). However, increased fatness resulted in lower yields of edible product (Nuti et al., 2003a), and retailers and their ethnic customers prefer goat meat with no fat (Karanjkar et al., 2000). Increased carcass fatness increased subsequent drip, evaporation, and cooking losses in meat from Angora and Boer goats (Schönfeldt et al., 1993b), but the shear force, collagen solubility, and cooking losses of LM were not different with combinations of low and high energy and low and high protein levels in diets for dairy goats (Gadiyaram et al., 2003). Intensive management with high energy intake by goats increased the juiciness, tenderness, and texture of the chevon, but general acceptability was lower than with grazing systems because the meat had higher fat (Karanjkar et al., 2000). This reinforced the report of Intarapichet et al. (1994) that the acceptability of goat meat was decreased with higher concentrate feeding because the flavor intensity was increased. Carlucci et al. (1998) found that meat from goats grazed and fed a commercial pellet was more tender and juicy, whereas meat from goats fed hay and a commercial pellet was stringier, with more meaty odor and flavor. Unsaturated fatty acids and lipid oxidation were higher, but PUFA were the same in meat from concentrate-fed Spanish and Spanish × Boer goats compared with meat from goats that were range-fed (Rhee et al., 1997). Male kid goats suckled on the dam had slightly more tender and juicy meat with a lower chroma value than meat from kid goats given milk replacer (Argüello et al., 2005). Undernutrition of young intact males did not influence dressing percents, but slaughter, carcass, and prime cut weights were less than with supplemented control goats (Almeida et al., 2000). Atti et al. (2004) determined the optimal level of CP in concentrate diets for growing goats to be 130 g/kg of DM, with no growth improvement in BW or lean deposition with higher levels of CP. A cobalt deficiency increased shear force and decreased muscle color in meat from male goats of Batina, Dhofari, and Jabal Akdhar breeds. Batina goats receiving hydroxocobalamin injections had muscles with lower shear force values, L* (darker color), expressed juice, and ultimate pH, and higher a* color (redder) than control goats (Kadim et al., 2004). Cooked meat from kid goats fed destoned olive pomace at 20% of the diet had the same proximate composition, color, and texture as meat from kid goats fed a concentrate pelleted control diet (Colonna et al., 2004). Supplementation with Tasco seaweed extract increased color stability of loin and rib chops during display in aerobic packaging, although there was no influence on lipid oxidation (Galipalli et al., 2004). Biogenic amines administered orally or in feed caused weight losses, whereas weaned control goats gained weight. Meat from treated goats had lower drip losses and redder meat compared with meat from control goats (Fusi et al., 2004). Feeding of cashew nut bran containing high amounts of oil and oleic acid did not alter the fatty acid composition of meat from intact and castrated male goats compared with control diets (Santos-Filho et al., 2005). Stress also may influence meat properties and the value of specific products. Two-hour transportation stress preslaughter did not alter water-holding capacity or shear force, but it decreased redness and chroma values in meat from young goats (Kannan et al., 2003). Older goats (24 to 30 mo of age) were more resistant to transportation stress than younger goats (6 to 12 mo of age), with no effect on a* and chroma values of loin cuts from the older goats. Cooking losses and shear force value in loin chops aged for 7 d were not affected by 2-h transportation stress (Kannan et al., 2003). Meat Processing Goat meat is sold primarily as whole carcasses or as bone-in cubes (Kannan et al., 2001) to ethnic consumers (Degner and Locascio, 1988; Pinkerton, 2002). Value is added to raw chilled meat by changing the form or utility. The Institutional Meat Purchase Specifications (IMPS) for Fresh Goat describe standard cutting practices for merchandising of uniform goat meat cuts (Olson et al., 1999; Pinkerton and McMillin, 2000; USDA, 2001). Meat properties and preservation are changed by many single or combination unit-processing operations. Primary processing operations include tenderization, grinding, flaking, freezing, and case-ready fabrication and packaging, whereas examples of further processing are curing, smoking, marinating, injection, emulsifying, forming, and cooking (Pearson and Gillett, 1996). Value-added product areas also would include irradiated products for microbial safety, precooked products for convenience, portioned and institutional items for uniformity, and nutritionally enhanced meat for healthfulness. Meat Tenderization Tenderization of raw chilled meat can be accomplished through enzymatic, electrical, and mechanical means (Romans et al., 2001). Postmortem endogenous proteolysis usually is associated with meat tenderization. Endogenous enzymatic activity decreased through 20 d of 5°C postmortem storage. Calpain-I and calpastatin activity decreased more than for calpain-II. Cathepsin B, B+L, H, and cystatin also fell by 9 to 35% after 20 d, whereas cathepsin D decreased 11 to 17% (Nagaraj et al., 2002). Maximal tenderization has been observed in the first 4 d postmortem, with decreased shear force at 8 d accompanied by increased myofibrillar index with storage time even though i.m. connective tissue was not changed (Kannan et al., 2002). Warner-Bratzler shear values were less with 6-d aging than 1-d aging of longissimus, biceps femoris, semimembranosus, and semitendinosus muscles (Kadim et al., 2003). Aging for 3 d did not improve tenderness, whereas aging for 14 d decreased shear force of gluteobiceps muscles from 11-kg goat carcasses (King et al., 2004). Simela et al. (2004) indicated that the tenderness and color properties of chevon were highly dependent on postmortem pH and temperature attained by the carcasses, with slow chilling and fast pH decline improving the tenderness and color. The postmortem pH decline in the King et al. (2004) study seemed to agree with this pH and temperature relationship; the pH and temperature measurements during chilling were not described in the Kadim et al. (2003) and Kannan et al. (2002) studies. Electrical stimulation has been shown to accelerate postmortem pH decline, hasten rigor development, and improve specific palatability characteristics (Seideman and Cross, 1982). The decreased shear force and increased sensory tenderness with 100-V, 5-ampere low-voltage electrical stimulation of goat carcass sides for 100 s was more in the longissimus than in semimembranosus and biceps femoris leg muscles. Overall palatability was higher, whereas sarcomere lengths, flavor ratings, and juiciness evaluations were not different with electrical stimulation (Savell et al., 1977). The increased tenderness of chops from goat carcasses electrically stimulated with 100 V and 5 amperes for 50 s was retained through a 7-d aging period compared with chops from control carcasses. Application of low-voltage electrical stimulation at different times during slaughter (after exsanguination, after pelt removal, after evisceration, after splitting) was equally effective in causing tenderization. High-temperature aging of carcasses, however, was less effective in tenderizing the longissimus, semimembranosus, and biceps femoris muscles than electrical stimulation (McKeith et al., 1979). Electrical stimulation had no effect on myofibril fragmentation or sarcomere length, but it increased tenderness at 1 and 3 d postmortem in cabrito carcasses (King et al., 2004). Mechanical blade tenderization decreased sensory connective tissue and decreased shear force in wholesale legs and loins, whereas cooking losses, cooking times, flavor, juiciness, and overall satisfaction were not changed from control cuts. Less tender cuts benefited more from mechanical tenderization than more tender cuts, but increases in the number of passes through the mechanical tenderizer only slightly improved sensory tenderness ratings (Bowling et al., 1976). Ground Goat Meat Ground meat products are popular minimally processed products, with ground beef accounting for 45 to 50% of retail beef sales in the United States (NCBA, 2001). Ground meat can be made by comminuting through a grinder knife and plate or through bowl cutting to achieve the desired size reduction (Aberle et al., 2001). James and Berry (1997) reported that the shear force was lower in comminuted goat patties made with grinding than with bowl cutter chopping. Ingredients may improve the properties or functionality of comminuted meat. Blending of 10 ppm α-tocopherol acetate into ground goat meat increased the water binding, odor scores, color stability, lipid stability, and shelf-life during 9 d storage at 4°C. A strong relationship between lipid and pigment oxidation was observed, with 10 ppm α-tocopherol acetate in ground goat meat extending shelf-life up to 7 d compared with 3-d shelf life in control samples (Verma and Sahoo, 2000). The addition of 15 to 50% oat bran to ground goat meat was shown to decrease moisture, fat, protein, Na, Zn, cholesterol, cooking loss, and shear force and to increase unsaturated fatty acids, soluble fiber, and insoluble fiber in patties. There were minimal composition and texture changes with 15 or 20% oat bran compared with control patties (Dawkins et al., 1999). Oat trim and oat gum were added to ground chevon at 0.5, 1, and 2% to provide meat products with added fiber and textural enhancement. Fat level and shear force were decreased, whereas tenderness and juiciness were increased with addition of the oat products (Dawkins et al., 2001). Packaging and Storage Oman et al. (2000) reported that the lean color score and overall appearance decreased as surface discoloration increased during 4-d storage of goat rib chops in retail overwrap packaging at 2°C, but there were no breed influences on those traits. Kannan et al. (2001) also found that although shoulder cuts were reddest, with the highest chroma and lowest hue, surface discoloration of all packaged cuts occurred within 4 to 8 d, so the case-life of goat meat was similar to other red meat species. Leg, shoulder/arm, and loin/rib cuts packaged in vacuum were slightly more tender than those in air-permeable film, with lower shear force in longissimus than in semimembranosus and triceps brachii (Kannan et al., 2001). The use of organic acid (2% lactic, 1.5% acetic, 1.5% propionic) sprays of inoculated goat carcasses increased refrigerated shelf-life by 5 d with marginal changes in color and odor scores. Total viable microbial counts of treated meat samples were decreased by 0.5 to 1.2 log units (Dubal et al., 2004). Oxygen-permeable packaging during 4°C storage increased the lipid oxidation of raw goat meat patties, but −20°C storage decreased the amount of lipid instability (Rhee et al., 1997). Vacuum packaging lengthened the shelf-life (28 d) compared with aerobic packaging (3 d) of minced goat meat, with lower aerobic microbial counts and higher semi-trained sensory panel acceptability also reported with vacuum packaged meat. Putrid odors in aerobically packed mince and sulfide odors in vacuum packs were observed during 4°C storage (Babji et al., 2000). Those results were reinforced by reports that vacuum packaging preserved the sensory quality of chevon patties more than aerobic packaging during 4°C storage, but the shelf-life in vacuum was not extended beyond 15 d in the study of Rajkumar et al. (2004). Lipid oxidation, shear force, and water activity did not vary with packaging type during 25 d of storage (Rajkumar et al., 2004). Further Processed Products Cooked Goat Meat Meat that is cooked and then stored refrigerated is susceptible to oxidation of lipids and phospholipids, known as warmed-over flavor (Cross et al., 1987). Refrigerated cooked chevon developed lipid oxidation, measured as hexanal, more rapidly than had been reported for other cooked meats, possibly due to the low fat content of goat meat (Lamikanra and Dupuy, 1990). The cooking yield and shear of goat leg chops were not different between broiling and microwaving, but broiled chevon chops were darker and lower in fat. The cooking yield and total work to shear patties cooked to an internal temperature of 75°C were higher with pan-frying than with broiling, which was higher than with baking (James and Berry, 1997). Cooking losses were highest in leg cuts, intermediate in shoulder/arm cuts, and lowest in loin/rib cuts (Kannan et al., 2001). McMillin and Brock (2004) described the linear dimensions, weight, color, and shear force for 11 of the major muscles in kid goat carcasses to provide baseline information for use of individual muscles in processing. Freezing of broiled goat meat patties in polyethylene bags, thawing, and reheating did not greatly decrease sensory scores. However, meat deboned at 3 to 4 h postmortem gave lower yields of broiled patties than did chilled meat (Padda et al., 1988). The lipid oxidation of cooked goat meat patties increased greatly during storage in air-permeable packaging at 4°C, but it increased only slightly in cooked patties stored at −20°C (Rhee et al., 1997). After frozen and thawed ground goat meat was cooked and then aerobically refrigerated for 0, 3, or 6 d at 4°C, lipid oxidation was higher in unseasoned cooked meat loaves than in seasoned chili. The brothy flavor intensity decreased and the cardboard flavor intensity increased as judged by trained sensory panelists, who evaluated unseasoned cooked goat loaves stored in oxygen-permeable packaging at each refrigerated storage interval (Rhee and Myers, 2003). Sausages Sausage products may be categorized by texture, ingredients, curing, smoking, casing type, size, and appearance (Pearson et al., 1996; Aberle et al., 2001). Uncured, seasoned linked sausages with 25 or 50% goat meat (remainder pork) had visual color, juiciness, and off flavor similar to that of 100% pork sausages, whereas the 100% goat sausages had higher color and off flavor scores. Sodium acid pyrophosphate decreased cooking losses and improved visual color in treated sausages compared with controls during the initial days of retail display (Reddy et al., 1987). Chevon sausage had lower fat, slightly lower cohesiveness, and the same gumminess and chewiness as beef and pork sausages, indicating that chevon could be used in manufacturing low-fat sausages without a major influence on textural attributes (Gadiyaram and Kannan, 2004). Cabrito smoked sausage containing 4% soybean oil and 0, 1.75, or 3% soy protein concentrate did not have flavor differences as judged by a trained sensory panel. Smoked sausage with 0 and 3.5% soy protein concentrate were similar in flavor, texture, and overall acceptance in a consumer sensory panel, but the cost of $13.50/kg was more than double the cost of comparable smoked pork sausage (Cosenza et al., 2003). Fermentation and drying are processing methods to preserve meat products. Fermented goat meat sausage (25% fat) with 0.5% rosemary as a natural antioxidant had increased lipid stability and higher untrained sensory panel acceptability compared with control fermented goat meat sausage during 70 d of storage in vacuum packages at 30°C (Nassu et al., 2003). Sausages such as frankfurters and bologna require extraction and solubilization of myofibrillar proteins to form a stable matrix with emulsified fat and water (Acton et al., 1983). Goat water-soluble and actomyosin proteins had higher emulsifying capacity than sheep, chicken, and pork proteins. Melted sheep and goat fat formed unstable emulsions due to poor dispersion of the excessive quantities of saturated fatty acids, but sheep and goat meat sausages may be used in place of pork and bovine meats (Chattoraj et al., 1979). Using the hind leg muscles of several species, goat and sheep proteins were found to be more extractable, with higher emulsifying capacities than proteins from the rounds of cattle and water buffalo. It was concluded that goat and water buffalo had some advantages over cattle meat for making an emulsion, but that goat meat should be mixed with water buffalo in manufactured products for the most stable products (Turgut, 1984). Emulsified goat sausages with 35% pork backfat or 25% shortening had the highest consumer acceptability. Higher fat levels in goat emulsion sausages gave lighter color, less firm texture, lower elasticity and springiness, and less intense smoky and seasoning flavor. There were no differences in “goaty” and “porky” flavors or overall desirability (Intarapichet et al., 1995). Mechanically separated meat recovered with mechanical deboning equipment has a fine texture suitable for emulsified sausages (Froning et al., 1971). Frankfurters made with mechanically deboned goat recovered from carcasses of old or young goats by auger-sieve separation had composition and processing characteristics similar to control beef and pork frankfurters. Consumer panelists preferred or did not dislike the frankfurters containing mechanically deboned goat or mutton when compared with control frankfurters with manually deboned beef and pork (Marshall et al., 1977). The mince recovered from intact shoulders, carcass frames after shoulder removal, and halves of goat carcasses was not different in composition, color, and lipid stability. The 5-mm openings in a belt-drum mechanical separator gave a coarser mince texture than 2-mm openings (McMillin et al., 1999). Goat Meat Product Acceptability Goat meat traditionally has been consumed by consumers from identified ethnic groups (Pinkerton, 2002). Foreign sensory panels gave higher scores to goat meat than domestic panelists, with loin chops rated juicier and more tender than leg steaks (Griffin et al., 1992). Meat from Anglo-Nubian crossbred goats was more acceptable, with less “goaty” flavor than meat from Thai native goats, whereas more intense and “goaty” flavor and lower acceptability was found in meat from goats fed higher levels of nutrition (Intarapichet et al., 1994). About 45% of the variation in meat from goats in intensive or extensive production systems was based on tenderness, juiciness, stringy, and cohesive sensory attributes, whereas 21% of the variation separated the samples on meaty attributes (odor and flavor; Carlucci et al., 1998). The flavor of cooked goat meat was affected by animal age, and although evaluations of goat leg meat tenderness were not affected by panelist age, sex, or ethnicity, the palatability was rated lowest by the youngest consumers and by those with the highest incomes (Dawkins et al., 2000). Goat meat and goat meat products have been compared with meat and meat products from other species. Goat meat had the same juiciness, but less tenderness and less overall satisfaction, as pork, beef, and lamb at comparable maturity and fatness (Smith et al., 1974). Sheep meat had higher palatability (Griffin et al., 1992) and had higher drip loss and juiciness (Schönfeldt et al., 1993b) than goat meat. Goat meat also was found to be less tender, have more residue, shear force resistance, and collagen content than sheep meat (Schönfeldt et al., 1993a). Sen et al. (2004) also reported that goat meat was less tender than sheep meat, although odor, juiciness, and overall palatability were not different. Goat meat flavor was the same as lamb, as reported by Gaili et al. (1972), whereas another study found that goat meat was less intense, tender, and juicy than lamb (Swan et al., 1998). Goat meat patties were distinguishable, but not different in acceptability, from lamb patties, although panelists deemed both to be soft and greasy, whereas goat and lamb curries were very acceptable (Swan et al., 1998). Patties from sheep were more tender, juicy, greasy, and less chewy than those from goat, with species-related “goaty” and “muttony” flavor being clearly distinguishable (Tshabalala et al., 2003). The “goaty” odor of goat meat has been attributed to 4-methyloctanoic (hircinoic) acid (Wong et al., 1975). The appearance of pan-fried chevon and beef patties did not change with different proportions of goat and beef. Consumer and trained sensory panels found similar juiciness, flavor, and tenderness in patties with less than 40% chevon and more than 60% beef, but increased levels of goat meat in patties increased cooking yield and shear force. It was suggested that goat meat could function as a lean meat source to augment product flavor (James and Berry, 1997). A consumer panel evaluated ground goat and mixed goat and rabbit (1:1) patties as similar in tenderness, juiciness, flavor, and acceptability, but lower in sensory properties, than rabbit patties (Dawkins et al., 2001). Frankfurters with 10, 25, or 40% mechanically deboned (separated) goat meat from young or old animals were preferred or not disliked compared with beef and pork control frankfurters (Marshall et al., 1977). Consumers preferred pork fat instead of shortening as the source of fat in emulsified goat sausages (Intarapichet et al., 1995). More than 66% of consumer panelists indicated that they would purchase smoked goat sausage (Cosenza et al., 2003). Consumers differentiated plain and seasoned goat from similar beef products, with similar sensory scores for beef and goat when goat was served before beef, but lower scores for goat when beef was served before goat meat (Rhee et al., 2003). This may explain the lack of processed or convenient goat meat products available in mainstream food markets. Nonetheless, a majority of university respondents who had eaten goat meat before would purchase goat meat in a supermarket or as an entrée from a restaurant, given the opportunity (Rhee et al., 2000). Lower price, taste, increased availability, and curiosity were given as circumstances when goat meat would be chosen over another meat (Rhee et al., 2000). A sensory map of meat from different species used for food consumption provided information about sensory properties, with sensory color attributes most important in describing differences between species. Goat meat was described as darker in color, with a distinct intense “gamey” flavor, toughness, and hardness compared with the meat from the 14 other species that were characterized (Rødbotten et al., 2004). Summary Value can be added at many points in the meat system of production, distribution, processing, and sale of goat meat products. Younger, leaner, and more heavily muscled goats are more valuable regardless of breed and diet, whereas increased goat age generally decreases meat tenderness and sensory properties. Most meat processing and preservation technologies can be used to produce goat meat products, with improved product consistency through uniform cutting and fabrication practices and sorting of raw materials. Goat meat provides improvements in emulsification, textural, and flavor properties that would be advantageous in lower fat or processed meat products, but oxidation of cooked goat meat and the specific product type influence storage and display shelf-life. Acceptability of goat meat and goat meat products is highly dependent on consumer culture and desires. The availability of more goat meat and more convenient product forms would add value in the marketing channels. Implications The potential for value-added goat meat items can be identified, but increasing the value to specific producers, processors, or consumers requires identification of and communication with the target consumers. There are opportunities for direct marketing of live animals or meat to customers or increasing the availability of traditional fresh raw chilled meat for the growing ethnic population. 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The next 25 years. Am. Demog.  25(3): 24– 27. Wilson, P. N. 1960. The effect of plane of nutrition on the growth and development of the east African dwarf goat. III. The effect of plane of nutrition and sex on the carcass composition of the kid at two stages of growth, 16 lb. weight and 30 lb. weight. J. Agric. Sci. (Camb.)  54: 105– 130. Google Scholar CrossRef Search ADS   Wong, E., C. B. Johnson, and L. N. Nixon 1975. The contribution of 4-methyloctanoic (hircinoic) acid to mutton and goat meat flavour. N. Z. J. Agric. Res.  18: 261– 266. Google Scholar CrossRef Search ADS   Footnotes 1 Presented at the ASAS Symposium: Goat Species: Export Potential, Market Outlook, and Value-Added Processing, St. Louis, MO, July 29, 2004. 2 Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as Publ. No. 04-18-0379. Copyright 2005 Journal of Animal Science

McMillin, K. W.; Brock, A. P.

doi: 10.2527/2005.8313_supple57xpmid: N/A

This review discusses adding value to goat meat, with an emphasis on the properties of goat meat and processed products. Goat meat value may be increased through production practices or meat processing. Decreasing the market channel steps or distribution costs and marketing animals in uniform or consistent groups will generally increase live animal value. Processing of meat into more palatable and usable forms or providing meat at times of higher purchaser demand will usually increase the price of the meat. Age, breed, and diet influence tenderness, juiciness, and flavor, with higher fat in carcasses and cuts from goats fed concentrate diets. The meat from kid and yearling goats of low conformation could be distinguished by goat meat consumers from the meat of goats with medium and high conformation. Ethnic groups that purchase goat meat have high levels of population growth and are increasing their buying power. Higher income populations desire value-added food products, which have been changed in form, function, or grouping to increase their economic value and/or appeal; however, lower income groups have a supply of imported frozen goat meat at a price lower than domestic sources. Food service operations purchase uniform cuts and sizes of meat, which are provided through USDA Institutional Meat Purchase Specification descriptions for goat meat. Goat meat also may be processed with unit operations similar to those for other meat species. Tenderness of domestic goat meat was improved with postmortem goat carcass aging, electrical stimulation of goat carcasses, and blade tenderization of goat cuts. The addition of α-tocopherol increased the oxidative stability of goat meat patties, whereas the addition of oat trim or oat bran decreased fat and shear force. Smoked and fermented goat meat sausages were acceptable to consumers, but they are more expensive per unit weight than sausages from other species. Emulsification capacity of goat meat proteins is high, and the palatability of frankfurters was increased with the use of mechanically separated goat mince. Goat meat was distinguishable from other species in plain and seasoned meat loaves, chili, curries, and patties. Specific organic acids are associated with goat meat flavor, and oxidized flavors develop more rapidly in cooked goat meat than in meat from other species. More convenient product forms and the availability of goat meat would increase the value and penetration of goat meat in ethnic and nontraditional consumer markets.

Andrews, F. M.;Buchanan, B. R.;Elliot, S. B.;Clariday, N. A.;Edwards, L. H.

doi: 10.2527/2005.8313_supplE18xpmid: N/A

Abstract Gastric ulcers are common in horses resulting in decreased performance and economic loss to the industry. Ulcers usually occur in the nonglandular mucosa of the stomach, which lacks adequate protection against the harmful effect of stomach acids. Also, performance horses are fed high hydrolyzable carbohydrate (grain) diets, which lower stomach pH and serve as substrates for resident fermentative bacteria, such as Lactobacillus spp. By-products of these bacteria include organic acids (VFA and lactic acid) that cause injury to the mucosa. This manuscript reviews the anatomy and barrier function of the stomach, and the causes and risk factors for development of gastric ulcers in horses. Introduction Gastric ulcers are common in horses, with prevalence estimated from 53 to 93%, depending on populations surveyed and type of athletic activity (Vastistas et al., 1994; Hammond et al., 1996; Murray et al., 1996). The gastric ulcers in horses are caused by many factors including, anatomy of the stomach, diet, restricted feed intake, exercise, stress (stall or transport), and the use of non-steroidal antiinflammatory agents. Because many factors are involved in the cause of ulcers, the term equine gastric ulcer syndrome (EGUS) has been coined to describe the condition of erosions and ulcerations occurring in the distal esophagus, nonglandular and glandular stomach, and proximal duodenum of horses (Andrews et al., 1999). This paper reviews the anatomy and barrier function of the equine stomach, causes and risk factors for EGUS, and current studies aimed at determining the pathogenesis of EGUS. Anatomy and Barrier Function of the Equine Stomach The proximal half of the equine stomach is covered by stratified squamous epithelium or mucosa (an extension of the esophagus) and approximately 80% of ulcers occur in this region (Andrews and Nadeau, 1999). Histologically, the nonglandular squamous mucosa consists of four distinct zones or cell layers; the outermost cell layer (stratum corneum) functions as a barrier to diffusion of strong electrolytes, such as sodium and HCl. The cells of the middle (stratum transitionale) and deeper (stratum spinosum) layers contain sodium-potassium ATPase, which functions in the transcellular transport of Na (Schnorr et al., 1971; Argenzio, 1999). The principle barrier to the diffusion of strong acids in the deeper layers consists of glycoconjugate substances containing bicarbonate, which is secreted by the superficial cells in the stratum spinosum. A minimal barrier of tight junctions between cells exists in the stratum corneum. The last layer is the stratum basale, which is one cell thick and presents no barrier to diffusion. These epithelial layers present a minimal physical barrier to acid (HCl and organic acids) diffusion compared with the glandular mucosa. Despite this minimal barrier function, in a recent study, a 30 mmol/L concentration of HCl (pH 1.5) exposed for 60 min was required to disrupt the barrier function in the horse squamous mucosa (Nadeau et al., 2003a,b). Thus, due to the mucosa's relative resistance to HCl damage, other acids in gastric fluid may act synergistically with HCl to disrupt this physical barrier. The distal half of the stomach is covered by glandular mucosa, which is responsible for secreting mucus, bicarbonate, hydrochloric acid (HCl), and pepsinogen (Murray, 1991). Approximately, 20% of gastric ulcers occur in this region of the stomach. This region of the equine stomach has extensive protective mechanisms consisting of a bicarbonate-rich mucus layer, an extensive capillary network, and a rapid ability for restitution or healing. Gastric ulcers occurring in this region are likely due to the breakdown of this barrier function from a stress-induced release of endogenous cortisol or the administration of nonsteroidal antiinflammatory agents. These agents cause a reduction in prostaglandins, which are important in maintaining mucosal mucus and bicarbonate secretion and maintaining blood flow to the epithelium. Cause of Gastric Ulcers in Horses Horses are continuous gastric HCl secretors, and acid exposure is thought to be the primary cause of gastric ulcers in horses. Also, performance horses are usually fed relatively low-roughage, high hydrolyzable carbohydrate diets and have a higher prevalence of gastric ulcers compared with pastured horses. Diets high in hydrolyzable carbohydrates provide substrates for gastric fermentation by resident bacteria. Gastric fermentation by-products, such as volatile fatty acids (VFA), alcohol, and lactic acid, may damage the squamous mucosa. Recently, several species of Lactobacillus were isolated from the stomach of horses, adding credence to this theory (Scott et al., 2003). Previously, an in vivo study in cannulated horses showed that an alfalfa hay/grain diet produced high VFA concentrations in the stomach (Nadeau et al., 2000). A stepwise model generated from those data showed that the presence of VFA (butyric, propionic, and valeric acids) and low stomach pH were important predictors of ulcer severity. Furthermore, an in vitro study with Ussing chambers showed that a 60 mmol/L concentration of VFA (acetic, propionic, butyric, and valeric acids) led to decreased chloride-dependent Na transport across the squamous mucosa and histologic changes of cell swelling (Nadeau et al., 2003a,b). In addition, Ca- and protein-rich diets, such as alfalfa hay, may protect nonglandular mucosa against acid injury (Nadeau et al., 2000). In a recent report, HCl alone and in combination with VFA caused inhibition of cellular chloride-dependent Na transport, cell swelling, and eventual ulceration when exposed to the nonglandular squamous mucosa at pH ≤4.0. The ulcergenic effects of the VFA in combination with HCl were pH, dose and chain-length dependent (Nadeau et al., 2003a,b). Bile acids were also shown to increase the nonglandular mucosal cell permeability to hydrogen ions, which eventually lead to ulceration (Berschneider et al., 1999). However, the effects of bile acids in EGUS is questionable because they usually come from less acidic duodenal reflux and are non-ulcergenic at a pH >4 (Argenzio, 1999; Berschneider et al., 1999). Pepsinogen, which is cleaved to pepsin at a pH <4, may have a role in the development of EGUS. This proteolytic enzyme may act with HCl to result in acid damage, but not synergistically (Widenhouse et al., 2002). Although HCl and stomach pH have been implicated as causes of EGUS, it is likely that a combination of HCl, organic acids, and pepsin act synergistically to cause EGUS. Risk Factors in Horses Although acid injury has been implicated in the cause of EGUS, several risk factors for its development have been identified (Murray et al., 1996; Andrews et al., 1999; Rabuffo et al., 2002). Exercise Intensity Horses in training and racing are at high risk of developing EGUS (Vatistas et al., 1999). Recently, it was shown that horses running on a highspeed treadmill have increased abdominal pressure and decreased stomach volume (Lorenzo-Figueras and Merritt, 2002). The authors speculated that stomach contractions allowed acid from the glandular mucosa to reflux into the nonglandular mucosa, leading to acid injury. Daily exercise may increase the exposure of the nonglandular mucosa to acid, explaining the increased prevalence of gastric ulcers in horses in race training. Furthermore, an increase in serum gastrin concentration has been shown to occur in exercising horses (Furr et al., 1994). This increase in serum gastrin may stimulate an increase in HCl secretion and lower stomach pH. Intermittent vs. Continuous Feeding Horses grazing at pasture have a decreased prevalence of EGUS. During grazing, there is a continuous flow of saliva and ingesta that buffers stomach acid, with stomach pH >4 for a large portion of the day. Conversely, when feed is withheld from horses, before racing or in managed stables, gastric pH drops rapidly and the nonglandular mucosa is exposed to an acid environment. Intermittent feeding has been shown to cause and to increase the severity of gastric ulcers in horses, and an alternating feed deprivation model was developed to produce EGUS experimentally (Murray and Schusser, 1993; Murray, 1994; Feige et al., 2002). The nonglandular mucosa is the most susceptible to ulceration in horses subjected to intermittent feeding due to its lack of mucosal protective factors. Studies have shown that stomach pH drops 6 h after feeding (Nadeau et al., 2000) and DM content decreases 12 h after feeding a mixed-feed diet compared with horses fed a hay diet (Coenen, 1990). Thus, horses should be fed hay continuously or every 5 to 6 h to buffer stomach pH. Diet Diet has been implicated as a risk factor for EGUS. Serum gastrin concentrations are high in horses fed high-concentrate diets. In addition, as noted previously, concentrate diets are high in hydrolyzable carbohydrates and are fermented by resident bacteria, resulting in the production of VFA, which, in the presence of low stomach pH (≤4), cause damage to the nonglandular squamous mucosa (Nadeau et al., 2003a,b). In another recent study in horses fed a high-protein and high-calcium diet (alfalfa hay/grain) showed higher stomach pH than horses fed a low protein and high-Ca (brome grass hay) diet. The high-protein, high-Ca diet had fewer and less severe gastric ulcers (Nadeau et al., 2000). Thus, feeding alfalfa hay may have some protective effect on the nonglandular mucosa in horses. Furthermore, horses fed mixed feed (128 g of CP and 175 g of crude fiber/kg of DM) for at least 14 d showed increased gastric ulcers in the nonglandular mucosa localized along the margo plicatus compared with horses fed a hay diet (Coenen, 1990). Thus, diets high in carbohydrates and protein have been implicated in causing gastric ulcers in horses. Transport Stress Transporting horses has been implicated as a risk factor for EGUS. Transportation of horses has been associated with dehydration, increased threat of respiratory illness (pleuritis, pleuropneumonia), and immune suppression (Watson, 2002). During transport, water and feed consumption is usually decreased which may cause an increased incidence of EGUS. Transportation has been shown to increase the severity of gastric ulcers in horses (MacAllister and Sangiah, 1993). However, a recent endoscopic study in Western performance quarter horses subjected to frequent travel and intensive training had a lower prevalence (40%) of EGUS than did horses in race training, calling into question the effect of transport on the development of EGUS (Bertone et al., 2000). Stall Confinement Stall confinement has been implicated as a risk factor for EGUS. Horses that are housed in pastures have a decreased prevalence of gastric ulcers compared with horses that are housed in stalls. The reason for this may be multifactorial, as horses that are stalled may be fed intermittently and housed without exposure to other horses (Feige et al., 2002). Nonsteroidal Antiinflammatory Drugs The nonsteroidal antiinflammatory drugs (NSAID), phenylbutazone and flunixin megulamine, have been shown to induce gastric ulcers in horses (MacAllister et al., 1993). However, the use of NSAID in racehorses has not been shown to be a risk factor for EGUS in multiple epidemiologic studies (Johnson et al., 1994; Murray et al., 1996; McClure et al., 1999; Vatistas et al., 1999; Rabuffo et al., 2002). However, in one study, NSAID caused ulcers in the glandular mucosa and increased the severity of ulcers in the nonglandular squamous mucosa (Murray, 1991). Thus, NSAID are thought to cause more severe ulcers in the glandular stomach mucosa because of their effect on prostaglandin inhibition. Prostaglandin inhibition by NSAID results in decreased mucosal blood flow, decreased mucus production, and increased HCl secretion. Although prostaglandins are also important in the regulation of acid production and sodium transport, it may be their effect on mucosal blood flow that is the most important (Navab and Steingrub, 1995; Barr, 2000). Adequate blood flow is necessary to remove hydrogen ions that diffuse through the mucus layer covering the glandular mucosa. Gastric mucosal ischemia may lead to a hypoxia-induced cellular acidosis, release of oxygen-free radicals, phospholipase, and proteases, which may damage the cell membrane leading to necrosis. Helicobacter Species Although Helicobacter species are an important cause of ulcers in other species, it has not been cultured from the horse. However, Helicobacter-specific DNA was isolated from the glandular and nonglandular mucosa of seven horses (Scott et al., 2001). The importance of this discovery is unknown and the role of Helicobacter spp. in EGUS remains speculative in light of other reports in which no organisms were seen in necropsy specimens from the stomach of horses with and without EGUS (Johnson et al., 1994). However, horses with chronic recurring gastric ulcers may benefit from antibiotic and antacid treatment in much the same way people with Helicobacter pylori infections have. Conclusions and Future Studies Equine gastric ulcer syndrome is caused by exposure of the stomach to inorganic and organic acids. Many factors including feeding, management, and stress allow increased production of these stomach acids that act synergistically to produce gastric ulcers. Volatile fatty acids (fermentation by-products of resident stomach bacteria), because of their high lipid solubility at stomach pH ≤4.0, enter into the nonglandular mucosal cells, acidifying the cell and damaging chloride-dependent Na transport, which results in cell swelling, necrosis, and ultimately, ulceration. Future studies should be directed at evaluating diets and dietary supplements that decrease or buffer secreted or fermented stomach acids. A recent study in ponies with chronic gastric cannulas showed that corn oil supplementation (45 mL/d orally) significantly decreased gastric acid production and increased prostaglandin concentration in gastric juice (Cargile et al., 2004). The authors speculated that corn oil added to the diet might impart protection to the stomach and prevent gastric ulcers. Furthermore, diets or supplements high in Ca and protein may buffer stomach contents and increase stomach pH, thereby preventing the damaging effects of HCl and organic acids. 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Google Scholar CrossRef Search ADS PubMed  Footnotes 1 Presented at the ASAS Symposium: Equine Carbohydrate-Associated Disorders, St. Louis, MO, July 26, 2004. Copyright 2005 Journal of Animal Science

Larson, R. L.

doi: 10.2527/2005.8313_supple37xpmid: N/A

The movement to price an increasing percentage of fed cattle on carcass merit grids has renewed interest in the effect of cattle disease on carcass traits. There is growing evidence that disease has the potential to affect not only carcass weight, but also the quantity, location, and ratio of muscle, fat, and water. A clear mechanistic pathway linking disease to changes in carcass traits has not been made. Three theories considered in this review are 1) a change in metabolic signals, such as cytokines and cortisol, could affect carcass composition through modification of hypothalamic secretions of thyrotropin-releasing hormone, by inhibition of IGF-I and insulin actions on muscle and fat tissues, and by direct protein catabolism and lipolysis; 2) disease-induced anorexia causing a decrease in serum IGF-I and an increase in serum GH, which induces a change in the partitioning of nutrients for tissue deposition; and 3) an indirect (and reversible) effect of anorexia, whereby sick cattle are on feed for fewer effective days than pen mates that do not become sick. Other pathogen or immune-mediated responses to disease, as well as interactions among hormones and cytokines, may influence nutrient partitioning and body composition but have yet to be described. The use of carcass merit to determine the value of fed cattle provides an improved economic signal of the cost of cattle disease. The value of disease avoidance as well as rapid diagnosis and treatment of disease increases when cattle are sold on carcass merit basis because of the negative effects of disease on carcass traits.

van der Steen, H. A. M.;Prall, G. F. W.;Plastow, G. S.

doi: 10.2527/2005.8313_supplE1xpmid: N/A

Abstract A relatively small number (less than 100) of DNA markers have been applied in swine breeding up to this point in time. Even so, these markers have been used for a range of different traits. Markers explaining variation in growth, lean percent, litter size, meat quality, susceptibility to developmental abnormalities, and even disease resistance have been identified and incorporated into breeding programs. Importantly, genomic and statistical tools have been developed to make use of the proliferation of genomic information that is now available. The ability to efficiently combine this information with quantitative genetics is the key to delivering continuing value for the swine industry. These DNA markers are analogous to a “turbocharger”—they work best with a good engine and chassis. Introduction Genetic improvement has, until very recently, been based on the “infinitesimal model,” which simply treats the genotype as a “black box” consisting of a very large number of genes, each of very small effect. This theory has been successfully implemented by animal breeders for many species, especially in the last 50 yr for cattle, pigs, and poultry. Milk yield and the cost of lean meat (from the input and output point of view) have changed remarkably as a result of these efforts (see Table 1). These changes are the result of genetic improvements combined with changing production systems. In particular, highly heritable traits, such as milk production in dairy cows and lean percentage in pigs and broilers, are predominantly improved through the genetic route. We now know that there is a finite number of genes (approximately 30,000 for pigs, a number though that is still very large and would justify the infinitesimal model). However, we also know that variation in some genes (or other sequences) can have a very large effect, with the “halothane gene” being the first example of a so-called major gene in pigs. But importantly, gene variants can make a significant contribution to quantitative variation, and these gene variants (alleles) can be identified and used within the genetic improvement program (see Table 2). The genotype at each of these loci provides information that can be incorporated into the genetic models to increase accuracy of estimated breeding values and the rate of genetic improvement, and possibly to more directly exploit the underlying biological effects involved. Table 1. Improvement of performance in livestock species from the 1960s to the present     Performancea  Species  Trait  1960s  Present  % change  Pigs  Pigs weaned/(sow•yr)  14  21  50    Lean, %  40  55  37    Feed conversion ratio (FCR)  3.0  2.2  27    Lean meat, kg/t of feed  85  170  100  Broilers  Days to 2 kg  100  40  60    Breast meat %  12  20  67    FCR  3.0  1.7  43  Layers  Eggs/yr  230  300  30    Eggs/t of feed  5,000  9,000  80  Dairy  Milk production/(cows•lactation), kg  6,000  10,000  67  Average    —  —  >50      Performancea  Species  Trait  1960s  Present  % change  Pigs  Pigs weaned/(sow•yr)  14  21  50    Lean, %  40  55  37    Feed conversion ratio (FCR)  3.0  2.2  27    Lean meat, kg/t of feed  85  170  100  Broilers  Days to 2 kg  100  40  60    Breast meat %  12  20  67    FCR  3.0  1.7  43  Layers  Eggs/yr  230  300  30    Eggs/t of feed  5,000  9,000  80  Dairy  Milk production/(cows•lactation), kg  6,000  10,000  67  Average    —  —  >50  a The figures vary greatly between regions and production systems, and the table provides an indication of the change, rather than accurate estimates. View Large Table 1. Improvement of performance in livestock species from the 1960s to the present     Performancea  Species  Trait  1960s  Present  % change  Pigs  Pigs weaned/(sow•yr)  14  21  50    Lean, %  40  55  37    Feed conversion ratio (FCR)  3.0  2.2  27    Lean meat, kg/t of feed  85  170  100  Broilers  Days to 2 kg  100  40  60    Breast meat %  12  20  67    FCR  3.0  1.7  43  Layers  Eggs/yr  230  300  30    Eggs/t of feed  5,000  9,000  80  Dairy  Milk production/(cows•lactation), kg  6,000  10,000  67  Average    —  —  >50      Performancea  Species  Trait  1960s  Present  % change  Pigs  Pigs weaned/(sow•yr)  14  21  50    Lean, %  40  55  37    Feed conversion ratio (FCR)  3.0  2.2  27    Lean meat, kg/t of feed  85  170  100  Broilers  Days to 2 kg  100  40  60    Breast meat %  12  20  67    FCR  3.0  1.7  43  Layers  Eggs/yr  230  300  30    Eggs/t of feed  5,000  9,000  80  Dairy  Milk production/(cows•lactation), kg  6,000  10,000  67  Average    —  —  >50  a The figures vary greatly between regions and production systems, and the table provides an indication of the change, rather than accurate estimates. View Large Table 2. Examples of marker application in the pork industrya DNA marker/Gene  Developer  Trait  First application  Reference  HAL1843 (CRC1)  Guelph/Toronto  Stress susceptibility; MQ; Yield/FC  1991  Fujii et al., 1991  ESR  ISU/PIC  LS  1994  Rothschild et al., 1996; Short et al., 1997  cKIT  Uppsala/PIC  Dominant white; Dam line development  1996  Johansson Moller et al., 1996; Marklund et al., 1998; Giuffra et al., 2002  MC4R  ISU/PIC  DG/FC/Lean  1998  Kim et al., 2000  FUT1  NADC/ETH  DR  1999  Meijerink et al., 2000  RN−/rn+ (PRKAG3)  INRA/Uppsala/Kiel; ISU/PIC  MQ  1997/1999/2000  de Vries et al., 1997; Milan et al., 2000; Ciobanu et al., 2001  IGF2  Liege/Uppsala  Lean  2002?  Jeon et al., 1999; Nezer et al., 1999; van Laere et al., 2003  MQ (several genes)  PIC and PIC/ISU  MQ  2001  Knap et al., 2002  CAST  ISU/PIC  MQ  2003  Ciobanu et al., 2002, 2004  RL, DA  PIC  RL, DA  2003  Plastow et al., 2003  DNA marker/Gene  Developer  Trait  First application  Reference  HAL1843 (CRC1)  Guelph/Toronto  Stress susceptibility; MQ; Yield/FC  1991  Fujii et al., 1991  ESR  ISU/PIC  LS  1994  Rothschild et al., 1996; Short et al., 1997  cKIT  Uppsala/PIC  Dominant white; Dam line development  1996  Johansson Moller et al., 1996; Marklund et al., 1998; Giuffra et al., 2002  MC4R  ISU/PIC  DG/FC/Lean  1998  Kim et al., 2000  FUT1  NADC/ETH  DR  1999  Meijerink et al., 2000  RN−/rn+ (PRKAG3)  INRA/Uppsala/Kiel; ISU/PIC  MQ  1997/1999/2000  de Vries et al., 1997; Milan et al., 2000; Ciobanu et al., 2001  IGF2  Liege/Uppsala  Lean  2002?  Jeon et al., 1999; Nezer et al., 1999; van Laere et al., 2003  MQ (several genes)  PIC and PIC/ISU  MQ  2001  Knap et al., 2002  CAST  ISU/PIC  MQ  2003  Ciobanu et al., 2002, 2004  RL, DA  PIC  RL, DA  2003  Plastow et al., 2003  a MQ = meat quality; FC = feed conversion; LS = litter size; DG = daily gain; RL = reproductive longevity; DA = developmental abnormality (e.g., susceptibility to hernia). ISU = Iowa State University; NADC = National Animal Disease Center, Ames, IA; ETH = Swiss Federal Institute of Technology, Zurich, Switzerland; INRA = Institut National de la Recherche Agronomique, France. View Large Table 2. Examples of marker application in the pork industrya DNA marker/Gene  Developer  Trait  First application  Reference  HAL1843 (CRC1)  Guelph/Toronto  Stress susceptibility; MQ; Yield/FC  1991  Fujii et al., 1991  ESR  ISU/PIC  LS  1994  Rothschild et al., 1996; Short et al., 1997  cKIT  Uppsala/PIC  Dominant white; Dam line development  1996  Johansson Moller et al., 1996; Marklund et al., 1998; Giuffra et al., 2002  MC4R  ISU/PIC  DG/FC/Lean  1998  Kim et al., 2000  FUT1  NADC/ETH  DR  1999  Meijerink et al., 2000  RN−/rn+ (PRKAG3)  INRA/Uppsala/Kiel; ISU/PIC  MQ  1997/1999/2000  de Vries et al., 1997; Milan et al., 2000; Ciobanu et al., 2001  IGF2  Liege/Uppsala  Lean  2002?  Jeon et al., 1999; Nezer et al., 1999; van Laere et al., 2003  MQ (several genes)  PIC and PIC/ISU  MQ  2001  Knap et al., 2002  CAST  ISU/PIC  MQ  2003  Ciobanu et al., 2002, 2004  RL, DA  PIC  RL, DA  2003  Plastow et al., 2003  DNA marker/Gene  Developer  Trait  First application  Reference  HAL1843 (CRC1)  Guelph/Toronto  Stress susceptibility; MQ; Yield/FC  1991  Fujii et al., 1991  ESR  ISU/PIC  LS  1994  Rothschild et al., 1996; Short et al., 1997  cKIT  Uppsala/PIC  Dominant white; Dam line development  1996  Johansson Moller et al., 1996; Marklund et al., 1998; Giuffra et al., 2002  MC4R  ISU/PIC  DG/FC/Lean  1998  Kim et al., 2000  FUT1  NADC/ETH  DR  1999  Meijerink et al., 2000  RN−/rn+ (PRKAG3)  INRA/Uppsala/Kiel; ISU/PIC  MQ  1997/1999/2000  de Vries et al., 1997; Milan et al., 2000; Ciobanu et al., 2001  IGF2  Liege/Uppsala  Lean  2002?  Jeon et al., 1999; Nezer et al., 1999; van Laere et al., 2003  MQ (several genes)  PIC and PIC/ISU  MQ  2001  Knap et al., 2002  CAST  ISU/PIC  MQ  2003  Ciobanu et al., 2002, 2004  RL, DA  PIC  RL, DA  2003  Plastow et al., 2003  a MQ = meat quality; FC = feed conversion; LS = litter size; DG = daily gain; RL = reproductive longevity; DA = developmental abnormality (e.g., susceptibility to hernia). ISU = Iowa State University; NADC = National Animal Disease Center, Ames, IA; ETH = Swiss Federal Institute of Technology, Zurich, Switzerland; INRA = Institut National de la Recherche Agronomique, France. View Large Animal breeders are interested in the association between alleles and traits of interest. The first step (Phase 1) in the process has been the definition of candidate genes, either directly or as “positional candidates” given results from QTL mapping studies. These genes are identified based on knowledge of gene function and expression and also ideally the position within the genome (e.g., in relation to the results of QTL studies). The increasing knowledge of the genome (from gene sequence or from expression studies) makes it possible to work on large numbers of candidate genes (“Phase 2”). This is based on the efficient identification of polymorphisms within populations for these genes and the study of associations between these polymorphisms (e.g., SNP) and traits of interest. For efficient implementation, this analysis should also consider an association with indirect or secondary traits, so that the real economic value of a marker can be established. It should be clear then, that both effective research and effective application are dependent on a program that integrates pedigree and phenotypic data collection with the genomics effort. For example, in the Pig Improvement Co. (PIC; Franklin, KY), genetic improvement is driven from a relational database containing pedigree-linked animals and their data (phenotypic, quantitative, DNA marker genotypes, and even functional genomics information) from farms across the world (more than 5 million animals will have been incorporated by 2004). This required the development of a suite of software tools that extract the maximum amount of information for each task (marker association analysis or the calculation of increasingly accurate estimates of breeding values expressed at the commercial level). Genomic results can be applied in three ways: more rapid accurate baseline improvement, commercial product differentiation, and new data to drive further research. This article will provide examples of applications for different traits and illustrate how the development of large numbers of markers across the genome (Phase 3) and functional genomics will provide new tools to affect traits that have been refractive to improvement by traditional methods. Results Phase 1 Genes within the leptin pathway represent candidate genes for traits such as feed intake, growth, and fatness. A DNA SNP was identified in the MC4R gene of pigs and found to explain variation in production traits in several breeding lines (Kim et al., 2000). The polymorphism resulted in a change in an AA in a highly conserved region of the protein, suggesting that the change was causative. However, initially, the effect within one of the populations tested (a Meishan synthetic line) was not significant, and the small effect for backfat observed with this population was in a direction opposite to that reported in the other lines. Even so, analysis of a larger dataset that took into account the potential for stratification within the populations seemed to confirm that the polymorphism was either causal or in very strong linkage disequilibrium with the causal mutation (Hernandez-Sanchez et al., 2003). Subsequently, similar results were obtained for the Meishan synthetic population, when additional data were added to the analysis, as those reported for the other breeding lines (Wilson et al., 2004). For example, the average difference between the homozygote genotype classes for days to 110 kg for the four pure lines reported in Kim et al. (2000) was 3.3 d, and it was 1.6 d for the Meishan synthetic line (Wilson et al., 2004). These results illustrate the importance of adequate sample size and also take into account potential admixture within populations when analyzing for marker effects. More recently, Kim et al. (2004b) presented results demonstrating that the original mutation may be causative by showing that the different MC4R alleles differ in their response to ligand binding using an in vitro gene expression system. Cells expressing both variants behaved very similarly in terms of ligand binding and cell surface expression; however, the Asn298 variant did not result in any increase in adenosine 3′,5′-cyclic phosphate content after binding of the ligand. Thus, it was concluded that this unconserved variant does not activate adenylyl cyclase. It is not surprising, therefore, that very consistent results have been obtained with this DNA marker in commercial crossbred genotypes as well as breeding lines. For example, Jungst et al. (2001) found additive effects of 0.07 kg/d for feed intake (P < 0.05) and 0.6 mm for backfat thickness (P < 0.05), and extended the findings to show improvements in loin depth (0.7 mm; P < 0.10) and primal yield (e.g., AutoFOM [SFK Technology A/S, Herlev, Denmark] ham, 0.11 kg, P < 0.05; and AutoFOM loin, 0.09 kg, P < 0.05) for the more efficient genotype. Similar results were obtained in the United Kingdom when boars were selected using MC4R genotype. In this case, offspring (several thousand) from boars of the “lean” genotype (associated with slower growth, lower feed intake and lower backfat) had approximately 1.5 mm less P2 backfat (P < 0.001) and 0.6% more lean in the carcass (P < 0.001; reported in Plastow, 2003b). More importantly, the frequency of the polymorphism is at an intermediate level in a number of breeding lines, so that the marker can be used effectively in selection for these traits. This illustrates how even a marker explaining a relatively small amount of the total variation (approximately 2 to 7% of the genetic variance according to the trait) can be used to select for products that perform significantly better at the commercial level. The effect is a combination of the size of the effect and the allele frequency in the populations of interest. For example, if the frequency of a preferred allele is close to fixation (>0.9) then the effect of selection for this allele in a population will be relatively small, whereas if it is at a low frequency then the potential for improvement is correspondingly greater. As one would expect, the studies of obesity in mouse and man have generated a large number of potential candidate genes (MC4R is an example) that can be investigated for effects on growth-related traits in pigs (Kim et al., 2004c). For example, polymorphisms in HMGA1, a gene involved in adipocyte cell growth and differentiation, were found to be associated with variation in backfat in several different populations of pigs (Kim et al., 2004c). A similar size of effect was observed as for MC4R, of approximately 0.9mm between the homozygous genotypes. Interestingly, there was no evidence of an interaction (P = 0.74) between the two genes, HMGA1 and MC4R, and the combined effect was approximately 1.9 mm between the extreme genotype classes (this is not always the case for all gene pairs; e.g., see Carlborg and Haley, 2004). In addition, important results have been obtained from QTL studies including the identification of variants at a paternally imprinted locus, IGF2, (Jeon et al., 1999; Nezer et al., 1999; Buys, 2003; van Laere et al., 2003) that explains variation in backfat thickness and muscle mass (in this case there is no influence on growth). Furthermore, the comparative approach has led to the identification of polar overdominance in pigs, similar to the “callipyge” effect observed in sheep but for fatness at one locus and loin eye area at a second locus (Kim et al., 2004a). These effects are of interest because of their non-Mendelian inheritance. For example, only the IGF2 allele inherited from the sire is expressed so that offspring of boars homozygous for the favorable allele of IGF2 are more muscled independent of the genotype of the dam at this locus. However, the favorable allele is at a relatively high frequency in commercial lines selected for leanness (Buys, 2003). The PIC and its collaborators have generated a panel of performance trait markers that are available for incorporation in the breeding program increasing the accuracy of calculation of estimated breeding values for these traits. One of the most important areas of potential for the application of genomics is in breeding animals that are less susceptible to disease (Plastow, 2003a). This potential is well illustrated with the results obtained with the FUT1 gene (Frydendahl et al., 2003). A polymorphism in this gene determines the susceptibility of pigs to Escherichia coli F18 (Meijerink et al. 2000), which causes scours and bowel edema disease in weaned piglets. Mortality can be up to 40% in naïve herds exposed to the pathogen. However, animals homozygous for the (recessive) resistant allele are completely resistant to infection by E. coli F18. Not only is mortality due to E. coli F18 decreased to zero, but the growth of the pigs is significantly higher than the surviving pigs of the susceptible genotype. In commercial trials, the difference in growth rate between the resistant and susceptible pigs surviving challenge was 0.07 kg/d (P < 0.001; M. A. Mellencamp, D. Sullivan, and S. B. Jungst, unpublished results). The FUT1 marker is a useful example of using a marker for product differentiation and solution of a customer problem. In 1999, PIC started a program called “EdemaGard” and began to deliver to customers' grandparent dam-line boars and gilts, selected for the resistant allele of FUT1 from among its regular dam-line populations. Parent gilts produced from these grandparents are resistant to E. coli F18. Simultaneously, parent boars, selected for the resistant allele from within PIC's leading sire line were delivered to the same customers. This process has meant that the proportion of homozygous resistant pigs flowing through the system has increased from 8% to its current level of 35%. More than five million commercial pigs with added resistance have now been produced. Customers who are reaching these levels are experimenting with removing vaccinations and feed additives, coming to rely solely on the genetic protection afforded by these homozygous resistant animals. In November 2001, Vansickle (2001) reported on one customer's experience with the EdemaGard program in an article entitled “Genetically resistant line stops E. coli cold.” The selection of animals with improved meat quality is another area where marker assisted selection can have a significant impact (see Meuwissen and Goddard [1996] for a comparison of the potential effect of markers on different types of trait). The first marker to be used in pig breeding, Hal1843, had an effect on meat quality, as the mutant allele was associated with PSE meat as well as porcine stress syndrome (Fujii et al., 1991). In this case, once the mutant allele was identified, it became an industry requirement to prohibit the allele as the pork industry treated the “gene” as a defect. Therefore, although the development of the DNA marker test added millions of dollars to the pork industry, in terms of value for breeding companies and producers, the effect was probably close to zero (this aspect of value is discussed in more detail in Plastow, 2004). A similar situation existed for the RN− mutation, another major gene that has a large effect on cooked ham yield. However, marker assisted selection allowed PIC to begin to select more effectively against the unfavorable allele in its Hampshire populations (de Vries et al., 1997), whereas other companies or countries simply terminated their Hampshire programs. Ultimately, the causative mutation was identified and the industry was able to remove the RN− mutation from remaining Hampshire lines (Milan et al., 2000). Pig breeding companies are now paying more attention to meat quality and are including quality traits as an integral part of selection programs to make simultaneous improvements in both quality and production traits (see de Vries et al., 1998; Knap et al., 2002). The development of the field of genomics has stimulated interest in breeding for meat quality and, as was mentioned above, this “trait” constitutes a classic case in which DNA marker-based selection is at its most efficient: where the trait cannot be measured on the selection candidate but instead needs to be measured at high costs on its relatives postmortem. Once a DNA marker has been shown to be associated with variation in the target trait, then it can be used to genetically type young animals for preselection before performance testing. This is a distinct advantage over sib slaughter schemes, which are increasingly difficult and expensive to implement (Knap et al., 2002). Sib slaughter schemes, however, will continue to be used and they will be important to identify new markers and for monitoring breeding lines in order to optimize the breeding direction. The advantage of incorporating markers into selection programs can then be sustained when new markers are identified to replace older markers that begin to reach fixation. The database builds up over time to provide a very useful resource for this purpose or further validation of DNA markers identified in experimental populations or to test candidate genes (e.g., in Phase 3 of marker development; see below). Recent examples of meat quality (MQ) marker effects include polymorphism in the genes for calpastatin (CAST) and PRKAG3 that are associated with quantitative variation in tenderness (CAST) and pH and color (PRKAG3) (Ciobanu et al., 2001, 2002, 2004). As with performance traits, PIC uses a panel of DNA markers for meat quality in its selection programs (see Table 1 in Knap et al., 2002). Again, as was the case for MC4R, these effects have been clearly demonstrated in commercial genotypes and commercial environments. For example, the amount of product that fails to meet specification for the Japanese market (high ultimate pH, low color) was decreased from approximately 14% to approximately 7% when a polymorphism in PRKAG3 (Ciobanu et al., 2001) was fixed in the slaughter generation in a trial undertaken in a commercial plant with nearly 1,500 pigs (A. Sosnicki, J. Bastiaansen, and G. Plastow, unpublished results). Phase 2 Functional genomics (e.g., transcriptomics, proteomics) offers another exciting route to finding and understanding the genes and pathways involved in processes of economic importance. These techniques and the tools that they provide allow for the identification of new candidate genes and potential DNA markers, but also the ability to study the interaction between genotype and environment. For example, an understanding of the basis of the resistance to E. coli F18 (a mutation in the gene, FUT1, encoding the enzyme α(1,2)fucosyltransferase; see above) indicates why all young pigs (before weaning) are phenotypically resistant: The gene is not expressed until after weaning. Significant functional genomics studies are now underway in the areas of disease susceptibility (e.g., for Haemophilus parasuis, Galina et al., 2002; Oliveira et al., 2003; www.pathochip.com; and for Porcine Reproductive Respiratory Syndrome virus (PRRSv)) and muscle/meat quality (e.g., Maltin and Plastow, 2004; Plastow et al., 2005; www.qualityporkgenes.com). Blanco and coworkers (I. Blanco, A. Canals, G. Evans, M. Mellencamp, N. Deeb, L. Wang, and L. Galina-Pantoja, unpublished results) found a genetic influence on the progression of H. parasuis infection in well-controlled challenge experiments. Tissue samples were collected from sites typically affected by H. parasuis infection for RNA preparation and analysis of gene expression. Animals were characterized according to their response to challenge and “resistant” or “susceptible” groups of animals compared with controls using microarrays fabricated with cDNA libraries generated from “defense” tissues of control and infected animals. Both known and unknown genes were identified as significantly up- or downregulated in treatment vs. control samples. The known genes identified are involved in signal transduction, protein biosynthesis, trafficking and turnover, transcriptional control, immune or inflammatory response, and cell cycle control (L. Galina-Pantoja, G. Evans, S. Dornan, C. Sargent, A. Canals, and J. Ullrich, unpublished results). These identities are encouraging, and the next step is to identify SNP within some of these genes for association analysis. This may lead to the identification of DNA markers that explain variation in susceptibility to H. parasuis and, in some cases, general resistance to disease, thereby providing new tools to select for healthier animals. The Quality Pork Genes project was created to identify genes associated with variation in different aspects of muscle quality and then to develop genetic tools that could be used to improve the quality of pork and processed pork products. The phenotypic database (on 500 animals and more than 400 traits) is complete; cDNA microarrays have been produced and gene expression and proteomic analysis is underway to search for genes explaining variation in water-holding capacity, i.m. fat content, and tenderness (Plastow et al., 2005). The database, project samples, and resources provide the opportunity to investigate a range of growth and quality traits. Those genes (or the pathways containing such genes) where variation in expression is associated with variation in the traits of interest will become candidates for SNP identification and association analysis. Ultimately, new markers will be generated and utilized in improvement programs or to provide product differentiation, as has already been achieved in Phase 1 (Knap et al., 2002; Ciobanu et al., 2001, 2004). The candidate gene approach clearly works as illustrated by the examples provided above. The success of this approach is based on the choice of the candidate genes, the quality of the data/DNA set and the willingness and ability to persevere, as success is not guaranteed for each project. The markers are based on causative mutations (Hal1843) or are likely to be causative mutations (e.g., MC4R, IGF2, FUT1, PRKAG3) or are closely linked markers (ESR or the first markers used to manage RN−) or less closely linked markers (most markers). Moving to Phase 3 The molecular tools that are now available make it possible to work on a relatively large number of candidate genes. This facilitates the development of several markers for each trait and line/breed of interest. Results of a multiple marker project are presented in Figure 1. The project involved multiple markers, traits, and lines, resulting in 4,500 estimates of a marker effect for a trait-line combination. Each result is characterized by the estimated size of the marker effect expressed in phenotypic standard deviation units (y-axis) and the significance of the effect, the P-value (x-axis). In general, significance increases as the size of the effect increases (as expected). The deviations of this general pattern are due to factors such as allele frequencies and sample size. The question is which results to take seriously. By taking a certain cut-off point for size of the effect and significance, we get results (Sector 1 of Figure 1) that are worthwhile to pursue. If this is set too liberally (Sector 1 is large), then too many false positive results are generated and resources are wasted in follow-up research. If, however, the cut-off-point is too restrictive (Sector 1 is small), then a large number of false negatives are generated and effects that are real are ignored. Clearly, there needs to be a balance between risk and resources. The multiple marker approach is still in development with many unanswered questions relating to interpretation of results, optimal use of resources and use of the markers in breeding programs. Figure 1. View largeDownload slide Results of a multiple marker project. Marker effects (Add/SD) and significance (P > |t|) for 4,500 estimates. Figure 1. View largeDownload slide Results of a multiple marker project. Marker effects (Add/SD) and significance (P > |t|) for 4,500 estimates. The next step in this development from one to many markers is the use of thousands of markers spread over the entire genome. Meuwissen and Goddard (2000) demonstrated that taking account of linkage disequilibrium among many marker loci in a genome-wide scan could more directly relate causative mutations to the individuals that carry them. The advantage compared with linkage analysis using adjacent pedigree depends on a number of factors, including population structure and history. However, for pig population structures, exploiting linkage disequilibrium promises to increase the power to map QTL, and should lead eventually to more accurate estimates of breeding value, and/or more direct exploitation of mutation effects. A different approach works on the hypothesis that sufficient markers can capture the entire genetic variation that exists for any heritable trait, without the need to nominate likely QTL. There may be potential to include much of the effects of both gene action and gene interaction (see Carlborg and Haley [2004] for examples and discussion of the importance of gene interaction and epistasis). This is still a very speculative concept. In theory, thousands of markers can be developed and used with a large set of phenotype data to “train” the markers to predict the breeding value of individuals. This approach can be useful in situations where trait recording is carried out intensively for a relatively short period of time, followed by a number of generations of selection on marker information (W. Muir, Genome Wide Marker Assisted Selection, Plant and Animal Genome, Poultry Workshop, San Diego CA, January 2004, personal communication). The model used, however, is much simpler than reality and the theory has not been tested with real data. The first target would be to develop an advanced version of BLUP and incorporate a large number of markers in the estimation of breeding values. Finally, genomics is contributing to the characterization of genetic diversity providing an important component for decisions on the conservation of pig breeds (Delgado et al., 2003) as well as providing tools for identity preservation or traceability. Indeed, the opportunity for genomics as well as for divergent breeds increases as greater product differentiation is required, and we should expect that it will enable the pig industry to identify and then use the gene variation that is contained within the large number of pig breeds found around the world. Both gene mapping and functional genomics may be mechanisms by which epistasis may be “tamed” for new product development. Traceability will also incorporate specific trait markers as participants in the chain as well as consumers will want confidence in the provenance of the products that they are purchasing (Delgado et al., 2003; Plastow, 2003b). Discussion As is illustrated previously, DNA markers are already being applied at a significant level in the swine industry today (see Table 2 for examples; we estimate that the number of markers in routine use is now more than 50). An additional example of how genomics is being used not only for product differentiation but also for ongoing product improvement programs is PIC's commercially successful 337-boar line, which sires a growing (already in double digits) share of all U.S. slaughter pigs. Its success derives from better meeting U.S. packer requirements for meat yield and pork quality, as well as producer needs for fast growth and economy. The 337 line is from a true hybrid line created by PIC, beginning in the 1970s, with at least four different breeds contributing to it at one time or another. The genotypes of a range of markers are determined early in life among all the piglets of this line. The information provided is then added into trait EBV for a more accurate estimate of breeding values and faster rates of genetic improvement of the line. However, knowledge of specific genotypes additionally allows for (and to the customer this is more immediately visible and tangible) product differentiation. One version of the 337 line is sold as a fast-growing customized line for high meat quality; it is selected with specific targets for a range of MQ markers. The line has already been developed and the resulting higher-MQ slaughter pigs from an 80,000-sow pyramid are already being harvested. Another version, on the market since 1999 and mentioned previously, is sold with homozygosity for the FUT1 resistant allele. Yet a third version, available since 2002, is sold for cost-conscious customers who want tangibly better feed conversion. In this case, the producer not only receives a boar with a high index value based on EBV, but specifically, the boar is homozygous for a marker that impacts appetite. It is important to note that the genomics components are added to an excellent product developed through the application of quantitative genetics. Thus, markers are analogous to a turbo-charger in car production: put a turbocharger on a Pinto and you still have Pinto that cannot outrun a Corvette. The work PIC has been conducting on meat quality since the beginning of the 1990s is already yielding outstanding products that combine fast-growing pigs that yield premium-quality carcasses at harvest. These products are already selected by incorporating DNA marker information in the improvement process. Projects such as Quality Pork Genes are beginning to add to the understanding of genes and gene interactions in growth and muscle development. This may lead to new insights that might impact human medicine as well as pork production (the identification of the RN− is an example; Milan et al., 2000). Implications This review describes how the pork industry has begun to use the first results from animal genomics research. Future breeding programs will involve more traits, more data, more genetic markers, and more science. However, the key to success will remain the effective incorporation of these elements into an effective breeding program that is implemented within the genetic improvement units to deliver products that perform on farm, in the abattoir and meat chain and on to the eating experience iteself. Genomics has already been applied to influence performance at each of these steps (e.g., the effect of variation in CAST on pork tenderness), and it will be applied with increasing impact in the future. The greatest effect, however, is likely to be in developing animals that are less susceptible to disease. 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Kronfeld, D. S.; Treiber, K. H.; Hess, T. M.; Boston, R. C.

doi: 10.2527/2005.8313_supple22xpmid: N/A

Specific quantitative methods for determining insulin resistance have been applied to obesity, activity/inactivity, reproductive efficiency, and exercise in horses, but only nonspecific indications have implicated insulin resistance as a risk factor or component of equine diseases. Insulin resistance derives from insulin insensitivity at the cell surface, which regulates glucose availability inside the cell, or from insulin ineffectiveness due to disruption of glucose metabolism inside the cell. Interplay of insensitivity and ineffectiveness should be considered in regard to patterns of disease, such as laminitis. Detection of insulin insensitivity is made weakly on the basis of fasting hyperinsulinemia, more strongly with a statistically validated surrogate, such as the logarithm of the reciprocal of basal insulinemia, or best by a specific quantitative method. Subjects found to be at risk can be managed to improve their insulin sensitivity by dietetics. Claims for dietetic prevention of a disease should be distinguished from claims for avoidance of a dietary risk factor. The evidence required for a claim of prevention is a controlled intervention trial as for a therapeutic drug, according to the U.S. FDA. In contrast, the evidence required for a claim of avoidance is association revealed by population studies plus causation shown by mechanistic experiments, as formulated in the Surgeon General of the Public Health Office's (1988) Report on Nutrition and Health. In this view, no appropriate evidence is available for the prevention or treatment of insulin resistance in an equine disease. Evidence is available, however, to justify avoidance of high-glycemic feeds, such as high starch intakes in grains, clover, and alfalfa, and high fructan intakes in grasses, to decrease the risk of acute digestive disturbances associated with rapid fermentation, and chronic metabolic disorders associated with insulin resistance. During submaximal exercise, high-glycemic meals have been shown to increase glucose utilization immediately. On the other hand, chronic adaptation to feeds that exchange corn oil and fiber sources for sources of sugar and starch confers benefits to athletic performance that may be due to several aspects of fat adaptation, including the regulation of insulin sensitivity, as well as glycolysis and lipid oxidation by signals from insulin receptors. Information regarding insulin resistance suggests methods for protecting health and promoting horse performance.

Olson, K. C.

doi: 10.2527/2005.8313_supple107xpmid: N/A

The purpose of this article is to discuss the relationship between range management practices and reproductive performance of beef cattle. The primary axis of this relationship is via the influence of range management on the nutritional status of the cow and the concomitant effect of nutritional status on reproductive status. Abundant research on beef cattle in confinement has established the relationship of nutritional status on reproductive status. Research evaluating beef cow nutritional responses to range management is more limited, and evaluations of reproductive responses to range management are even fewer. Grazing management practices that influence beef cow performance include stocking rate, grazing distribution, and grazing systems. Stocking rate has the greatest influence, with heavy stocking rates diminishing a cow's ability to select and consume a highly nutritious diet. This limitation on nutrient intake decreases the cow's reproductive performance. Range management to improve grazing distribution effectively increases forage supply by enticing cows to consume underutilized forage, thereby altering the stocking rate relationship in favor of supporting more cows or higher nutrient intake by individual cows. Grazing systems that involve multiple pastures so grazing and rest can be scheduled among the pastures have variable effects on cattle performance, but they decrease performance more often than not compared with continuous grazing. The limitation of the pasture area to which cattle have access in a grazing system effectively decreases the forage supply, and can thereby decrease diet selection and nutrient intake. Alternative forages, especially complementary forages that grow in the early spring, can dramatically improve cow nutritional status during the critical pre-and postpartum periods of the annual beef cow production cycle. Supplementation, particularly the use of protein with low-quality forages, can augment beef cow reproductive status, as long as it is managed in concert with proper grazing management. In conclusion, various range management practices can have positive or negative effects on beef cow nutrition and reproduction. Range management needs to be carefully planned and implemented to ensure that it contributes to efficient reproduction.