Journal of Animal Science

Jones, F., T.;Langlois, B., E.;Cromwell, G., L.;Hays, V., W.

doi: 10.2527/jas1984.583519xpmid: 6370946

Summary Swine from two herds with different histories of antibiotic exposure were fed diets containing 0 or 55 mg of chlortetracycline (CTC)/kg. One of five pigs in each herd-diet treatment group was infected orally with Escherichia coli strain BEL15R that was resistant to nalidixic acid (NA), chloramphenicol (C), streptomycin (S), sulfamethizole (TH) and tetracycline (TE). Effects of CTC on the quantity and duration of fecal shedding of E. coli BEL15R and on the transmission of strain BEL15R and its R-100 plasmid from infected pigs to uninfected pigs and chicks were determined. Quantity and duration of shedding were greater in infectedantibiotic-herd pigs than in infected nonantibiotic-herd pigs. Feeding of CTC increased the duration of shedding in infected pigs from both herds. Strain BEL15R colonized and was shed in one uninfected antibiotic pig in each treatment group, but it did not colonize in any of the uninfected nonantibiotic-herd pigs or in the uninfected chicks. In vivo transfer of resistance to C, S, TH and TE occurred in the infected antibiotic-herd pigs but not in the infected nonantibiotic-herd pigs. Transfer of the R-100 plasmid occurred from the infected to the uninfected antibiotic-herd pigs and to the uninfected chicks housed near the antibioticherd pigs fed CTC, but not to the chicks housed with the antibiotic-herd pigs fed the control diet. No transfer of resistance occurred from the infected nonantibiotic-herd pigs fed either CTC or control diet. This content is only available as a PDF. Author notes 3 Present Address: Dept. of Poul. Sci., North Carolina State Univ., Raleigh, NC 27650. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Cole, N., A.;Hutcheson, D., P.;McLaren, J., B.;Phillips, W., A.

doi: 10.2527/jas1984.583527xpmid: 6715267

Summary Two trials were conducted to determine the influence of preshipment zeranol implant and protein and urea levels of the feedlot receiving diet on the performance of yearling steers. In each trial, one-half of the steers were implanted with 36 mg of zeranol 30 d before shipment from El Reno, Oklahoma to Bushland, Texas. In trial 1, receiving diets were fed for 14 d and contained 10.6 (LP), 12.6 (MP), or 16.0% (HP) crude protein (DM basis). A fourth diet contained 10.8% protein with 7% of total N from urea (LPU). In trial 2, receiving diets were also fed for 14 d and contained 12.4 (MP) or 16.7% (HP) protein. Two other diets contained about 16% protein with either 15% HPMU) or 30% (HPHU) of total N from urea. After 14 d on the receiving diets, calves were fed a 70% concentrate intermediate diet for 7 d and were fed an 85% concentrate finishing diet until the end of both trials. Zeranol implants did not significantly affect marketing-transit weight changes, but increased (P<.05) daily weight gains at all time periods in both trials. In trial 1 on d 14, steers fed the HP diet tended (P<.10) to have faster gains and greater gain/feed than steers fed the LP and LPU diets, with steers fed the MP diet being intermediate. On d 56 of trial 2, steers fed the HP receiving diet for 14 d tended (P<.10) to have faster gains and had higher (P<.05) gain/feed than steers fed the MP and HPHU diets, with steers fed the HPMU diet being intermediate. Overall, performance from arrival to slaughter was not affected by protein or urea levels in the receiving diet. This content is only available as a PDF. Author notes 2 USDA-ARS, Bushland, TX 79012. 3 Texas A&M Univ. Res. and Ext. Center, Amarillo, TX 79106. 4 Dept. of Anim. Sci., Univ. of Tennessee, Knoxville, TN 37901. 5 USDA-ARS, El Reno, OK 73036. 6 Mention of a trade name or product does not constitute a recommendation or endorsement for use by the USDA. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Pitman, W., D.;Hodges, E., M.;Peacock, F., M.

doi: 10.2527/jas1984.583535xpmid: N/A

Summary Pastures of Sarasota stargrass, Callie Bermuda grass and Bigalta limpograss were evaluated in comparison with the currently recommended forage cultivar in South Florida, Ona stargrass, by year-long grazing with yearling steers. Pastures, 2 ha in size, were divided into four .5 ha units and rotationally grazed at initial stocking rates of five 200 kg steers/2-ha pasture. A “put-and-take” stocking system was used to adjust animal numbers beyond the initial stocking rate to maintain relatively uniform levels of standing forage. Differences in individual animal performance were not obtained among grasses over a 3-yr period. However, carrying capacity during the warm season differed (P<.01) with 975, 969, 829 and 739 animal days of grazing for Sarasota, Ona, Callie and Bigalta, respectively, during this 230-d period. Beef production of 619, 607, 513 and 532 kg/ha on pastures of Sarasota, Ona, Callie and Bigalta, respectively, differed only at the P=.18 level, but this is probably of economic importance. Average daily gain was closely correlated (r=.419 for Bigalta to r=.577 for Ona with P<.0001 for each of the four grasses) with forage in vitro organic matter digestibility (IVOMD). However, equations involving forage IVOMD and forage quantity did not account for much more of the variation in animal performance than did IVOMD alone. This content is only available as a PDF. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Hale, O., M.;Newton, G., L.;Cleveland, E., R.

doi: 10.2527/jas1984.583541xpmid: 6715268

Summary Littermate gilts were used to study the effects of exercise during the growing-finishing period on performance, age at puberty and conception rate. In trial 1, 12 gilts walked 15 min daily on a treadmill 6 d/wk (Monday through Saturday) until they attained body weights of about 100 kg, while 12 littermate gilts were not forced to exercise. Initial weight and age averaged 24.7 kg and 74 d, respectively. For trial 2, 12 gilts walked 30 min daily 6 d/wk (Monday through Saturday) on a treadmill, while 12 littermate gilts were not exercised. Initial weight and age of these gilts averaged 26.8 kg and 76 d, respectively. The treadmill was operated at 0 slope and at a speed of 2.6 km/h. Within trial, there were no differences (P>.05) in weight gain, average daily gain, feed consumed, feed to gain ratio, average backfat depth or loin eye area between gilts exercised and those not exercised. In both trials, there were no differences (P>.05) in age at puberty between exercised and nonexercised gilts. In trial 2, 10 gilts were selected in each of the exercised and nonexercised groups and were hand-mated to the same boar on the second estrous cycle. Eight gilts from the exercised group conceived, while nine from the nonexercised group conceived. Four gilts from the nonexercised groups had severe locomotor problems while only one gilt from the exercised groups had difficulty walking. This content is only available as a PDF. Author notes 1 Dept. of Anim. Sci. 2 Rural Development Center, Tifton, GA 31793. 3 Supported by State and Hatch funds allocated to the Georgia Agr. Exp. Sta. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Zollinger, W., A.;Nielsen, M., K.

doi: 10.2527/jas1984.583545xpmid: 6715269

Summary Genetic trends for weaning weight were evaluated in 15 purebred herds in the United States participating in the Angus Herd Improvement Records production testing program. Regression techniques were used for separate estimates of sire and dam contributions that were summed to estimate total herd trend. Sire contributions, calculated as the pooled within sire regression of weaning weight ratio on year of calf birth, ranged from .01 ± .23 to 1.30 ± .24 across the herds and averaged .51 ratio units/yr. Dam contributions, estimated as the pooled within dam regression of offspring weaning weight ratio, deviated from the contemporary paternal half-sib average ratio, on year of calf birth, ranged from .06 ± .06 to .68 ± .11 and averaged .34 ratio units/yr. A positive trend in direct effects was associated with a possible negative trend in maternal effects. The annual trend within herds ranged from .21 to 1.50 ratio units and averaged .85 units over all herds, representing 1.8 kg annual genetic gain in weaning weight. This content is only available as a PDF. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Zollinger, W., A.;Nielsen, M., K.

doi: 10.2527/jas1984.583550xpmid: 6715270

Summary Field records (53,989) from the American Angus Association were used to evaluate the impact of bias associated with genetic trend in estimated breeding values for weaning weight. Annual estimates of breeding values were calculated using the reported weaning weight ratios and ratios adjusted for estimated genetic trend. Genetic gains were assumed to be consistently linear. Bias was estimated as the difference between the two estimates, and herd averages across years for dam's bias ranged from .38 to 3.86 ratio units. The bias was a function of the magnitude of the estimated trend and the generation interval. The impact of this bias was small in young cows, but increased rapidly after their fourth or fifth calves. When annual genetic trend was less than .75 ratio units, the loss in selection response (based upon selecting the top 10 and 50% of males and females, respectively) did not exceed 2.5%. In herds with trends between .75 and 1.1 units/yr, the loss was 6 to 8%. In the five herds where estimated trend exceeded 1.1 units/yr, the loss ranged from 10.8 to 25.2%. This content is only available as a PDF. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Zollinger, W., A.;Nielsen, M., K.

doi: 10.2527/jas1984.583556xpmid: 6715271

Summary Field records from 15 herds involved in the Angus Herd Improvement Records program of the American Angus Association indicated that positive assortative mating for weaning weight estimated breeding value (EBV) was being practiced. For each dam, a separate EBV was calculated from information on each progeny with all other progeny data deleted. Individual, paternal and maternal half-sib data available in all years were included in each calculation and thus, were held constant. Bias in cow EBV caused by nonrandom mating was measured as the pooled within dam regression of dam EBV on progeny's sire EBV deviated from the contemporary sire average EBV. Across herds, the average estimated bias associated with positive assortative mating ranged from .05 to .08 ratio units. This content is only available as a PDF. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Notter, D., R.;Ferrell, C., L.;Field, R., A.

doi: 10.2527/jas1984.583560xpmid: 6715272

Summary Effects of breed and intake level on growth and feed efficiency in ram lambs were tested with 52 Rambouillet, 46 Dorset and 53 Finnish Landrace (Finn) rams. Rams were individually fed at 100, 85 or 70% of ad libitum or at maintenance. The experimental diet contained 79% digestible dry matter (DM), 3.28% N and 2.95 Mcal metabolizable energy/kg DM. Rams were serially slaughtered every 35 d for 175 d. The efficiency of deposition of body weight, protein, energy and trimmed cuts was determined by breed and intake level over constant time, weight, fat and maturity intervals. Ranking of the breeds for feed efficiency depended upon both the interval and the criterion of evaluation. Efficiency of protein and trimmed cut gain was positively related to mature size in the time and weight intervals, but all differences in efficiency were small in the fat or maturity intervals. Gross energetic efficiency did not differ greatly among breeds in any interval. Dorsets appeared to have a somewhat greater propensity to fatten than the other breeds and to be less able to retain N at a fixed N intake. In the constant time interval, maintenance requirements were estimated to be 115 kcal/kg.75, and the estimated partial efficiencies of energy deposition in fat and protein were .49 and .26, respectively. This content is only available as a PDF. Author notes 1 Roman L. Hruska U.S. Meat Animal Research Center, AR-SEA, USDA. 2 Present address: Dept. Anim. Sci., Virginia Polytechnic Institute and State Univ., Blacksburg 24061. 3 Division of Anim. Sci., Univ. of Wyoming. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Malik, R., C.

doi: 10.2527/jas1984.583577xpmid: 6370947

Summary A review is presented of the genetic and physiological aspects of growth, body composition and feed efficiency in mice. The genetic parameters considered are: nature and extent of within and between-line genetic variation for body weight and growth rate-, direct and correlated responses to selection for body weight, weight gain, feed intake and feed efficiency; direct genetic effects of the offspring (gO); maternal genetic effects (gM); heterosis in the offspring (hO); maternal heterosis (hM), and recombination effects in the offspring (rO). The physiological parameters considered are energy requirements for maintenance and growth. The role of thermoregulatory thermogenesis in relation to the partitioning of metabolizable energy between maintenance and growth requirements of large and small mice is emphasized. The relationship of feed efficiency with other traits is reviewed at length. This content is only available as a PDF. Author notes 1 Present Address: Faculty of Agriculture, versity of Papua New Guinea, P.O. Box 793, Papua New Guinea. 2 Dept. of Anim. Sci. Copyright 1984 by American Society of Animal Science. American Society of Animal Science

Gunsett, F., C.;Andriano, K., N.;Rutledge, J., J.

doi: 10.2527/jas1984.583591xpmid: N/A

Summary The precision of estimates of realized genetic parameters obtained from multiple-trait selection experiments is considered. Statistical optimality theory is used in conjunction with Monte-Carlo techniques to investigate the relationship between index weights and the variability of the estimates. Results indicate that arbitrary choice of index weights is ill advised, and that with some prior knowledge (or good guesses) about the magnitudes of the genetic parameters, index weights can be identified that yield estimates with predictable variation. This content is only available as a PDF. Author notes 2 Dept. of Meat and Anim. Sci., Univ. of Wisconsin, Madison 3 Dept. of Dairy Sci. and Dept. of Statist., Univ. of Wisconsin, Madison. 4 Present address: Dept. Anim. Sci., North Carolina A and T Univ., Greensboro, NC 27411. 5 Present address: Sandoz Pharmaceuticals, Rt. 10, Box 11, East Hanover, NJ 07936. Copyright 1984 by American Society of Animal Science. American Society of Animal Science