Journal of Animal Science

Flowers, W. L.

doi: 10.2527/animalsci2002.0021881200800es10008xpmid: N/A

The influence of the number and quality of spermatozoa inseminated on litter size in swine is examined in this paper. There is evidence to support the following observations. Litter size varies among boars when insemination doses contain the same numbers of spermatozoa. Increasing the number of sperm inseminated generally has a positive effect on the number of pigs born alive, especially between the range of 1 to 3 × 109 cells. The manner in which litter size responds to increasing the number of spermatozoa inseminated varies among boars. These relationships between the number of sperm inseminated and the resulting litter size provide credence to the idea that boars exhibit unique fertility patterns. These divergent fertility patterns probably reflect variability in the ability of spermatozoa from different boars to fertilize ova. A number of semen quality tests have been developed to estimate the fertility of semen. Several of these have documented that increases in estimates in sperm quality are associated with increases in litter size. However, the relative effectiveness of each of these for determining the optimal number of spermatozoa that should be included in insemination doses remains to be elucidated. In summary, increasing the fertilization rate of boars should be possible by improving semen quality, increasing the number of spermatozoa inseminated, and adjusting using estimates of sperm quality to adjust number of sperm inseminated. However, the magnitude of changes in litter size resulting from these strategies is likely to vary considerably among boars.

Purcell, W. D.

doi: 10.2527/animalsci2002.0021881200800es10012xpmid: N/A

Price systems in the beef industry have failed to communicate needed changes to producers. The lack of alignment between what is produced and what consumers want and are willing to pay for pushed beef demand down nearly 50% from 1980 through 1998. Ineffective grades allowed the price-driven system to fail, and current public policy blocks needed changes in quality grades for fresh beef. Product attributes of importance to consumers, such as tenderness, have not been identified and brought into the pricing process. In the presence of a failed pricing system, producers have looked to pricing grids, contracts, and vertical alliances to be paid for value and for investments in genetics and technology. The future will see continued competition between price-based systems and non-price means of coordination and quality control. If grades are not modernized and new technology brought in to allow more Contracts, Coordination, Prices attribute identification, the price-based system will continue to disappear. Producers will need to look at alternatives and find the approach that allows them to participate in a beef system that profits from better serving a discriminating and changing consumer. Packers have revised their business models as contractual arrangements and alliances have allowed them to coordinate what they buy with needs for new consumer-friendly products and to accomplish at least a modicum of quality control. Once low-cost commodity operations, the large beef packers are now more nearly quality-oriented. The huge investments in new products and markets they have made are the catalysts that have turned the beef demand picture to the positive. Those investments are important to the industry and will set the future of the beef industry for the year 2010 and beyond. The future of beef can be very positive if needed changes are made to ensure the consumer is better served.

Cárdenas, H.; Pope, W. F.

doi: 10.2527/animalsci2002.0021881200800es10007xpmid: N/A

Follicular recruitment and atresia are important processes associated with ovulation rate in swine. Follicle-stimulating hormone regulates granulosa cell division, differentiation, and steroidogenic function, and, as such, significantly influences follicular growth and development. Follicle-stimulating hormone is an inducer of follicular recruitment in swine and an inhibitor of granulosa cell apoptosis, and it seems to be a major regulator of ovulation rate in swine. Although local factors, such as growth factors and steroid hormones, might regulate follicular development by controlling the expression of gonadotropin receptors or by modulating other related processes, the dominant role of FSH cannot be ignored. Recent results indicate that androgens might be among the local factors regulating ovulation rate in swine. Administration of testosterone or the nonaromatizable androgen dihydrotestosterone increased the number of ovulations in gilts in a dose-dependent manner. Furthermore, administration of dihydrotestosterone increased the amounts of FSH receptor mRNA in pig preovulatory follicles. Steady-state amounts of FSH receptor mRNA are relatively high during the early follicular phase but decrease significantly as follicles grow and approach ovulation, suggesting that major changes in amounts of FSH receptor mRNA occur during late follicular development in pigs. Local ovarian factors that regulate follicular responsiveness to gonadotropins seem to be important components of the mechanisms that control ovulation rate in pigs.

Beermann, D. H.

doi: 10.2527/animalsci2002.0021881200800es10004xpmid: N/A

Mechanisms by which ractopamine and other beta-adrenergic agonists stimulate skeletal muscle growth are discussed. Oral administration dose-response studies in surgically altered laboratory animals provide evidence that indirect endocrine-mediated effects are not an essential component of efficacy. Results from age-comparison studies in laboratory animals and livestock species provide evidence that metabolic maturity of skeletal muscle may be a critical factor with regard to efficacy, suggesting that receptor presence and density are important. Temporal studies demonstrate the rapidity of responses associated with protein and lipid metabolism changes, and that progressive decline in rate of anabolic response in skeletal muscle results from chronic administration. Associated results that demonstrate progressive beta-adrenergic receptor density reductions are observed and suggest, likewise, that protein accretion rate and muscle growth rate responses are receptor-mediated. Measurement of in vivo metabolic effects resulting from continuous systemic infusion has been conducted in relatively few experiments. Detailed blood flow and hind limb net flux data are available for a single beta-agonist, cimaterol. Kinetics studies and close arterial infusion of cimaterol in the hind limb of growing cattle demonstrate large transient increases in amino acid extraction from the circulation and similar patterns of net uptake when compared with the contralateral control saline-infused hind limb. Predictions of differential net effects on protein accretion using integration of essential amino acid net flux measurements are corroborated by quantitative documentation of protein mass differences in individual muscles from treated and control hind limbs. Definitive descriptions of specific pathway mechanism(s) of action for increasing protein synthesis have not as yet been reported. Therefore, additional research is required for elucidation of cellular and intracellular components of mechanism(s) of action.

Dantzer, R.

doi: 10.2527/animalsci2002.0021881200800es10002xpmid: N/A

Although the concept of welfare makes reference to feelings of individual animals, the exact nature of these feelings and their relationship to emotions and cognitive abilities of the animals under consideration are never detailed. Based on the concepts of stress and coping, an extensive list of indicators of physical health, production, behavior, and physiology has been set up for the purpose of recognizing good from bad welfare. However, these indicators do not allow us to make any inference about mental states. This issue is important because welfare considerations apply to farm animals of different species and, within a given species, to animals of different ages, which are likely to have varying degrees of emotional and cognitive capacity. In the past, disagreements about exact definitions of emotion and cognition have blurred the matter and hampered research. However, this should no longer be the case; the study of emotions and feelings has emerged as a field of active research in psychology and neuroscience over the last two decades. It is now possible to go over philosophical discussions on the nature of feelings and to set up a research agenda on emotion and cognition in farm animals that should help us to understand their welfare requirements.

Held, S.; Mendl, M.; Laughlin, K.; Byrne, R. W.

doi: 10.2527/animalsci2002.0021881200800es10003xpmid: N/A

The purpose of this paper is twofold. First, it discusses in general terms how animal production can be affected by the animals' cognitive abilities; second, it aims to introduce our work on pig cognition. We suggest that livestock cognition does not only affect production indirectly through its effects on livestock welfare, but also that cognition can have direct effects. Direct effects are evident when cognitive abilities limit feed intake, for example, or in the recognition of groupmates or offspring. We illustrate such direct effects with two case studies from pig production: voluntary feed intake after weaning and production losses associated with aggression in groups. Voluntary feed intake after weaning is affected by preweaning experiences, weaning age, and postweaning practices. Some studies suggest a link between early environment and cognitive development in piglets, as has previously been demonstrated in other species. We suggest this as a possible contributing factor to low feed intake immediately after weaning. The other case study centers on aggression in groups of pigs. Several studies indicate that some social assessment and recognition take place between individuals, allowing them to judge each other's aggressiveness and to avoid fighting once a dominance hierarchy has been established. However, the regrouping of previously familiar pigs can also lead to high aggression levels. This suggests that pigs may be able to form only short-term social memories, or that some aspects of their social memory are disrupted before regrouping. Our work shows that pigs have well-developed spatial memory abilities, which can be disrupted by common management procedures. If this were also the case for social memory, it could help explain increased aggression levels in previously familiar pigs after routine procedures. We also show that pigs are able to adjust their foraging behavior depending on the presence or absence of a subordinate, exploitable co-forager that knows where food is. This ability has potential implications for the way feed is best dispensed to pigs such that all group members can maximize their intake.

Ford, S. P.; Vonnahme, K. A.; Wilson, M. E.

doi: 10.2527/animalsci2002.0021881200800es10010xpmid: N/A

Prenatal losses in U.S. pig breeds range from 30 to 50%, of which greater than 75% occurs before d 30 of gestation and is thought to result from littermate asynchrony. Numbers of embryos can be experimentally increased to d 30 using superovulation (excess ova shed) and superinduction (transfer of embryos to an already pregnant uterus); however, these females farrow the same number of pigs as untreated controls. These data demonstrate that between d 30 and parturition there are significant additional periods of conceptus loss, which has led to the conclusion that uterine capacity (i.e., the number of conceptuses a sow uterus can accommodate) is the major limitation to litter size in the pig. The special importance of uterine capacity in the pig may result from the noninvasive epitheliochorial type of placentation in this species, making the surface area of attachment between the placenta and endometrium a limiting factor. In devising selection schemes for this trait, one could logically conclude the selection for either longer uterine horns or for a reduced conceptus size should potentially increase litter size in the pig. Researchers have evaluated the impact of differences in prepubertal uterine horn length on subsequent uterine capacity using a unilateral hysterectomy-ovariectomy model but have had modest and variable success in increasing litter size at farrowing. In contrast, results from our laboratory suggest that placental size is moderately heritable and results in consistent increases in litter size of two to three pigs in the Yorkshire breed with little impact on pig birth weight or neonatal viability. This selection of pigs for smaller and relatively more efficient placentae (i.e., the number of grams of fetus that can be supported by 1 g of placenta) seems to provide a useful method for increasing litter size in the pig. A careful evaluation of the physiologic and genetic differences of conceptuses with differing placental efficiencies is necessary if we are to determine specific factors affecting litter size in the pig.

Mersmann, H. J.

doi: 10.2527/animalsci2002.0021881200800es10005xpmid: N/A

β-Adrenergic receptor (βAR) agonists reduce body fat in mammals and birds. Synthetic lipid metabolism is decreased in βAR agonist-treated animals or in agonist-treated adipocytes in vitro. Degradative lipid metabolism is increased by βAR agonists in adipocytes in vitro and in vivo. The βAR agonist effects are blocked by βAR antagonists. In mammalian tissues, there are at least three distinct βAR subtypes; β-1 (β1AR), β-2 (β2AR), and β-3 (β3AR). Individual tissues have different proportions of subtypes. For example, greater than 85% of the βAR in rat heart is β1AR, in guinea pig lung is β2AR, and in rat adipose tissue is β3AR. Subtype distribution within a tissue varies with species (e.g., human heart has 65% β1AR and porcine adipocytes have less than 10% β3AR). There is species variation in the amino acid sequence of a βAR subtype. Thus, it is expected that some βAR agonists would have different effects in the same tissue in different species because of different βAR subtype distribution and(or) amino acid sequence. In support of these concepts, the pharmacology of βAR agonists and antagonists in adipocytes is in many cases species-specific. Cloning of individual βAR subtypes allows determination of the pharmacology of subtypes from that species. For example, the pharmacology of the cloned porcine β1AR, β2AR, and β3AR indicates selected agonists or antagonists can be used to assess the proportion of βAR subtypes. Nucleic acid sequences of the subtypes were used to prepare probes to quantify the subtype mRNA. The pharmacological and mRNA data agree rather closely and indicate porcine adipocytes contain over 70% β1AR. The effects produced by a βAR agonist (or antagonist) on adipose tissue in vivo depend not only on the species and the adipocyte βAR subtype distribution, but also on the pharmacokinetics and pharmacodynamics of the compound in that species, including blood flow to the tissue, and the multiple metabolic and endocrine effects of the compound in other tissues of the body. In short, it is expected that individual βAR agonists would have somewhat different effects in different species.

Mills, S. E.

doi: 10.2527/animalsci2002.0021881200800es10006xpmid: N/A

Receptor-mediated signals are tightly regulated by feedback inhibition and act to prevent signal overload and to reset the receptor to a changing environment. Short-term regulation (uncoupling) of beta-adrenergic receptors (βAR) involves receptor phosphorylation and uncoupling of the receptor from the G protein Gs. Chronic exposure to ligand leads to reduced receptor number (down-regulation), which results from a combination of receptor internalization and degradation, and decreased mRNA abundance. The extent of βAR regulation is subtype-specific with a rank order of β2AR > β1AR > β3AR. Differences between species are expected also because amino acid sequences differ. Uncoupling and down-regulation of βAR in pig tissues has been demonstrated in vivo and in vitro, although skeletal muscle exhibits a blunted response compared with adipose tissue and changes in mRNA abundance have not been observed. Desensitization presents a challenge clinically in the treatment of human disease and may well limit the effectiveness of βAR ligands used to promote livestock production. Pigs fed βAR ligands show a rapid response in growth and feed efficiency that tends to peak during the first 7 to 10 d but declines thereafter toward zero by approximately 6 wk. A similar pattern was reported in rats fed clenbuterol and was accompanied by a 50% reduction in βAR in skeletal muscle. Feeding clenbuterol every 2nd d prevented the decline in the response to clenbuterol and gave a growth response that was equivalent to daily dosing. These data suggest that strategies to prevent or circumvent βAR down-regulation may prolong the agonist response. Intermittent dosing of pigs may present logistical problems. An alternative approach may be to incrementally increase the dose of βAR ligand to compensate for the decline in response or to augment the ligand response by inhibiting the inhibitory G protein Gi.

Lay, D. C.; Matteri, R. L.; Carroll, J. A.; Fangman, T. J.; Safranski, T. J.

doi: 10.2527/animalsci2002.0021881200800es10011xpmid: N/A

A limited ability to cope with environmental stressors (cold, disease, limited nutrition), particularly over the first 2 to 3 d of life, predisposes the piglet to relatively high rates of neonatal morbidity and mortality. Due to the serious economic impact, numerous surveys of preweaning losses have been conducted over the last century. Although losses are still significant, the existing literature indicates a significant improvement in piglet survival over time, as determined by reports of 35% preweaning mortality in 1924 and 13 to 15% in 2000. Major sources of mortality have been categorized as overlying by the sow, insufficient energy intake, and disease. Causes of mortality may be more closely linked with one another than previously believed. Interactions exist between disease, thermoregulation, and nutrition. Piglets with disease and nutritional problems experience hypothermia and express altered behaviors that increase the likelihood of their being laid on by the sow. High probabilities of neonatal losses are associated with low birth weights, cold ambient temperatures, and scouring. An understanding of the interactions between environmental stressors and the biology of the piglet forms the basis for strategies and recommendations for improving preweaning survival.