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Sheep are seasonally polyestrous breeders, meaning they breed when day length shortens in the autumn. Ewes respond to changing day length through chemical pathways involving melatonin receptors. Some breeds, such as Dorset, are known to be less seasonal with many ewes able to breed and lamb year-round. The Melatonin Receptor 1a (MTNR1A) gene was identified as a candidate gene controlling out-of-season lambing. The first studies in the Cornell STAR accelerated lambing flock found that a MTNR1Aallele was associated with a shorter time to first lambing and a shorter period between lambings. The favorable allele was denoted the Mallele and the unfavorable allele, the mallele. This study evaluated additional data for the effect of the Mn1Ipolymorphism on sheep reproduction. Genotypic frequencies among the 320 sheep in this study differed between Romney and breeds selected for accelerated lambing (P< 0.02), but they did not deviate from Hardy-Weinberg equilibrium. Using 228 ewes from the Cornell University flock, we found no association (P> 0.05) between the Mallele and success for out-of-season lambing and no significant differences were observed in several production measures, such as number of lambs delivered per yr or number of lambs weaned (P> 0.05). With few mmewes in the flock, these results may be due to the high level of selection for accelerated lambing. This study shows that the Mallele may not be a beneficial marker for use within flocks seeking to improve production and the ability to lamb out-of-season. These findings warrant additional research on the genetics of aseasonality in sheep.

Ability to select service sires that minimize partial or complete losses of pregnancy could have major economic impacts in sheep production systems. This study tested the null hypothesis that survival of potential progeny did not vary with breed type of service sire or among individual rams. Data included 980 ewes on 10 farms; each ewe was pregnant to 1 of 67 rams of 12 breeds. Number of conceptuses was estimated once during pregnancy by ultrasonography, either transrectal (embryos) or transabdominal (fetuses), and was compared with number of lambs born to estimate losses. Data were examined first for number of lambs born and second for documented losses. Individual service sires affected number born (P< 0.001), which varied from 0.70 to 2.45 lambs per pregnant ewe. The main effects of breed type on lambs born were not significant, but breed types of both service sires (P< 0.0002) and ewes (P< 0.001) interacted with diagnosed number of conceptuses. Lambs born varied with ewe age (P< 0.0001) and among farms (P< 0.0001), and statistically, farms interacted with number of diagnosed conceptuses (P< 0.0001); season had no effect. In documented losses, there were both main effects of individual service sire and a service sire × number of diagnosed embryos interaction (P< 0.005). Thus, ewes bred to some rams were more apt to lose single pregnancies, whereas ewes bred to other rams were more apt to lose 1 or more embryos or fetuses from multiple pregnancies. Breed type of service sire affected (P< 0.05) prenatal death. Complete losses of single conceptuses tended to be greater in ewes bred to black-faced or hair-type rams (service sire breed type × number of diagnosed conceptuses; P< 0.09). Breed type of ewes also varied in incidence of complete losses (P< 0.05); hair-type ewes (46%) lost more (P< 0.02) documented conceptuses from examination to birth than black-faced (27%), white-faced (20%), or dairy-type (25%) ewes. Greater losses of singles than of multiples occurred in black-faced (37% vs. 18%) and hair-type (64% vs. 27%) ewes than in other breeds (ewe breed type × number of conceptuses; P< 0.03) per ewe. Surprisingly, purebred conceptuses were lost less often (24%) than crossbreds (36.4%; P< 0.002). Selection of rams based on records of prenatal losses in ewes they serviced may be a method to decrease embryonic and fetal wastage. However, further study to determine repeatability of differences among service sires from year to year will be required.

The response to melatonin expression is one way that circadian rhythms of many biological processes are regulated. To evaluate the relationship between the melatonin receptor 1A (MTNR1A) gene and reproductive performance, records were compared in Dorset and 3/4-Dorset × 1/4-East Friesian ewes expressing different genotypes at the MTNR1Agene in the Cornell University sheep flock. There were 116 ewes with first lambing records, consisting of 91 Dorset and 25 crossbred ewes. Of these, 104 ewes had second lambing records. Genotypes were determined by PCR amplification of a fragment of the ovine MTNR1Agene followed by digestion with MnlIand RsaIrestriction enzymes. The effects of breed, year of birth, season of birth or season of first conception, and each polymorphism on days to first lambing and days between first and second lambings were evaluated. Our results show that ewes with at least 1 Mallele are able to conceive at younger ages, better able to breed and conceive out-of-season, and have shorter intervals between first and second lambings than ewes expressing only the mallele. The results presented in this study show, for the first time, an association of the MTNR1Agene and lambing frequency and confirm the importance of the MTNR1Agene as a potential DNA marker for out-of-season breeding.

Thirty-nine Holstein steer calves were assigned to one of five treatments at birth and individually fed for 200 d with milk replacer reconstituted to equal the fat and protein concentration of beef cow milk. Treatment levels were the quantities of reconstituted milk fed per day based on lactation curves, which were based on peak milk levels (PML) of 2.72, 5.44, 8.16, 10.88, and 13.6 kg/d, respectively. In addition to reconstituted milk, chopped alfalfa hay was offered ad libitum to allow for maximal voluntary forage consumption. All calves were fed a high-energy diet postweaning until they reached a similar degree of fatness in the 12th rib (4 to 5% chemical fat) as determined by ultrasound. There were differences (P< 0.05) among groups in weaning weight, preweaning ADG, age, and weight at slaughter. During the preweaning phase, there was a linear relationship (P< 0.01) for daily milk and forage DE intake; however, DE intake per unit of BW did not differ across treatments (P= 0.06). Increasing PML resulted in a linear (P< 0.01) decrease in alfalfa hay intake in the preweaning phase, and G:F increased quadratically (P< 0.01). During the postweaning phase, preweaning milk intake had no meaningful effect on postweaning ADG, but overall ADG had a linear relationship (P< 0.01) with preweaning milk level. There was no effect of PML on the 12th-rib lipid percent, marbling score, or quality grade, but protein and fat concentration in the carcass and empty BW increased linearly (P< 0.01) with PML. The group fed at 2.72 kg/d PML was 58 kg lighter (P= 0.03) and required 34 d more (P< 0.01) to reach the predetermined degree of fatness at slaughter than the group fed at 13.6 kg/d PML, suggesting that increased milk production by the dam can decrease the number of days to the slaughter weight at which a similar rib lipid concentration is reached.

Testosterone is known to act differentially on skeletal muscle from different regions. Two genes likely to mediate the testosterone effect are IGF-I, an important growth regulator acting in an autocrine and paracrine way, and androgen receptor (AR), as receptor density could account for differential muscle growth. Another muscle-specific gene that may play a role in differential muscle growth is myostatin, a member of the transforming growth factor-β superfamily, shown to be a negative regulator of skeletal muscle mass. The objective of this study was to quantify and compare the expression of these three genes in two different skeletal muscles in sheep. East Friesian × Dorset-sired ram lambs from Dorset ewes were used in a 2 × 4 factorial experiment. Eighteen sets of twins were assigned to four age groups corresponding to 77, 105, 133, and 161 d of age, and one individual from each set was castrated at birth. Total RNA was extracted from samples of splenius (SP) and semitendinosus muscles collected at the time of slaughter. Insulin-like growth factor-I mRNA was measured using competitive reverse-transcription PCR. Androgen receptor and myostatin mRNA were measured by ribonuclease protection assay with standard curves. Weight of SP was greater than semitendinosus in rams compared with wethers at 105, 133, and 161 d (P= 0.05, P= 0.04, and P= 0.02, respectively). The difference in IGF-I mRNA levels between the two muscles was greater in rams than in wethers at 133 (P= 0.001) and 161 d (P= 0.014), and the difference in AR mRNA levels was greater in rams than in wethers at 105, 133, and 161 d (P= 0.002, P< 0.001, and P< 0.001, respectively), with greater abundance in the SP. No difference was found in myostatin mRNA level between the two muscles in rams and wethers at any age. These results suggest that locally produced IGF-I and the regulation of AR expression are important for sexually dimorphic muscle growth patterns.

Two 3 × 2 factorial growth trials and a companion metabolism trial with 13, 15, or 17% dietary CP (DM basis), with or without 3% of the DM replaced with slowly degraded menhaden fish meal, were conducted to determine if level of dietary protein influences whether slowly degraded protein improves lamb growth and protein use. The growth trials included 32 and 34 pens of two weanling lambs initially weighing 23 to 26 kg and fed for 42 d. The metabolism trial included 12 additional lambs fed in metabolism cages with a 2-wk adjustment period, a 1-wk preliminary period, and a 7-d collection period. Plasma urea N (PUN) was measured in all lambs at the conclusion of the second growth trial and at the end of the metabolism trial. There was a protein level × protein source interaction (P= 0.05) for PUN of the 12 lambs in the metabolism trial but not for the 68 lambs in the second growth trial. Replacement of part of the soybean meal protein with protein from fish meal did not affect ADG or G:F at any protein level, but it lowered (P= 0.08) PUN in the second growth trial. Plasma urea N values were higher (P= 0.002) in lambs fed diets with 15 or 17% CP; however, ADG (P= 0.037 in Exp. 1 and P= 0.055 in Exp. 2), and G:F (P= 0.094 in Exp. 1 and P= 0.003 in Exp. 2) were lower for lambs fed the diets with 13% CP. There was little difference in ADG or G:F between lambs fed the diets with 15 or 17% CP, suggesting that a CP level of 15% with supplemental protein from soybean meal would be optimal for 25- to 40-kg growing Finnsheep × Dorset lambs.

Testosterone is known to act differentially on skeletal muscle from different regions of the body. Two genes likely to mediate the testosterone effect are insulin-like growth factor I (IGF-I), an important growth regulator acting in an autocrine and paracrine way, and androgen receptor (AR), because receptor density could account for differential muscle growth. Another muscle-specific gene that may play a role in differential muscle growth is myostatin, a member of the transforming growth factor-beta superfamily, shown to be a negative regulator of skeletal muscle mass. The objective of this study was to quantify and compare the steady state expression of these three genes in two different skeletal muscles in sheep. Eleven Dorset rams were slaughtered after reaching puberty and total RNA was extracted from samples of semitendinosus and splenius muscles. Insulin-like growth factor I mRNA was measured using a competitive reverse-transcription-polymerase chain reaction. Androgen receptor and myostatin mRNA were measured by a ribonuclease protection assay (RPA) with standard curves. The means (attomoles/μg RNA) for splenius and semitendinosus muscles were 1.39 and 1.02 (SE = 0.14), 4.05 and 2.96 (SE = 0.24), and 4.30 and 3.85 (SE = 0.37) for IGF-I, AR, and myostatin, respectively. The difference between the two muscles was significant for IGF-I and AR mRNA levels with higher levels in the splenius but not significant for myostatin. Our results show that locally produced IGF-I and the regulation of AR expression may be important for sexually dimorphic muscle growth patterns.

Growth, nucleic acid, and protein concentrations were measured in three muscles of 20 rams, 20 wethers, and 20 wethers implanted with testosterone. Two lambs from each group were slaughtered at 14-d intervals from 49 to 133 d, and then at 28-d intervals until 217 d, for a total of 10 slaughter ages. Immediately after slaughter, the semitendinosus, splenius, and triceps brachii muscles were removed, trimmed of adhering fat, and weighed. The DNA, RNA, and protein concentrations of these muscles were determined. Testosterone increased combined weight of the three muscles. The splenius muscles of rams and wethers implanted with testosterone were heavier and had a biphasic growth pattern as the combined muscle weight increased, whereas the splenius muscle of wethers had a single growth phase. Rams and implanted wethers had greater splenius muscle DNA and RNA concentrations than wethers as muscle weight increased. This model could be used to study the gene regulation of testosterone-induced muscle growth with the possibility of invoking similar effects in more economically important muscles.

A total of 110 Holstein steer calves 8 wk to 12 wk old were used in two trials to quantify feed energy and protein utilization by calves recovering from underfeeding protein. Three treatments (low protein, energy restriction and high protein) were imposed during the first two periods of growth (Period 1 was 154 d in Trial 1 and 112 d in Trial 2; Period 2 was 98 d in both trials). At the end of Period 1, calves in each treatment were fed either the low or high level of protein. All were full-fed a high-energy diet from the end of the second period until slaughter (estimated 26% body fat). Initial, end-of-period and final body composition were determined to calculate energy and protein retention. Compensatory gain was observed in all but one previously restricted group during realimentation; growth rates were 14 to 30% higher than controls. Degree of restriction altered the amount of compensatory gain; those that gained less during low-protein feeding gained faster during recovery. Compensating calves consumed more feed per unit metabolic body weight. Efficiency of gain (gain/feed) always was higher for the compensating groups, with no differences (P> .10) in overall efficiency. The restricted groups required 12 to 117 more days to reach a similar percentage final body fat. Final weight at a constant fatness was reduced by 44 kg when growth was restricted for 112 d at .12 kg/d followed by 98 d at .18 kg/d.

Four growth trials were conducted to determine whether lambs have the ability to recognize a dietary Ca deficiency and to correct that deficiency by consuming minerals offered free choice. In trial 1, lambs were fed a control or Ca-deficient diet with 0, 1, 5 or 10 mineral choices, only one of which provided Ca. Daily gains and feed efficiencies of lambs fed control diets tended to be superior to those of lambs fed Ca-deficient diets. Consumption of free choice calcium carbonate was greater (P<.05) for lambs fed Ca-deficient diets than for those fed control diets. However, total Ca intake was greatest (P<.05) for lambs fed control diets. In trial 2, lambs were fed diets containing .35, .20 or .06% Ca with zero or four mineral choices in either a constant or varied location. Daily gains were highest (P<.05) for lambs fed the control diet. Performance of lambs fed diets deficient in Ca was not improved by providing free choice minerals. Although free choice Ca intakes were higher (P<.05) for lambs fed Ca-deficient diets, total intake of Ca decreased with severity of dietary Ca deficiency. In trial 3, lambs were fed a (1) Ca-adequate diet, (2) Ca-deficient diet, (3) Ca-deficient diet with four mineral choices (one of which contained Ca) or (4) Ca-deficient diet with seven times the daily Ca requirement offered once weekly. Lambs fed control diets gained faster (P<.05) than those fed deficient diets with free choice minerals. Ca intakes were greater (P<.05) for control lambs than for those fed Ca-deficient diets with Ca available free choice. In trial 4, lambs were fed either a control or a Ca-deficient diet for 42 d. All lambs were then offered both control and Ca-deficient diets in separate compartments of the feed bunks. Although performance, bone and serum data followed trends similar to those observed in trials 1, 2 and 3, differences between treatment groups were not significant. Data from these trials support die recommendation that, when possible, required minerals should be provided in the diet rather than on a free choice basis.

Angus steers were fed one of six daily levels of antibiotic in supplements: control (no added drug); 183 mg monensin; 83, 175 or 220 mg lasalocid, or 149 mg lasalocid in mycelium cake. Alfalfa cubes and .57 kg of supplement were fed individually to five or six steers by means of electronic feeding doors. Cube consumption was ad libitumabove daily consumption of supplement. Orthogonal contrasts of the five degrees of freedom for supplement additives showed that cattle fed monensin ate less (P<.01 and gained more slowly (P<.005) than cattle fed lasalocid. This result was possibly caused by the steers' aversion to monensin supplement, which, in turn, decreased dry matter intake too drastically for them to maintain adequate energy intake above maintenance for efficient growth. Lasalocid affected growth rate, feed efficiency and plasma glucose in a quadratic (P<.025) manner; steers fed 175 mg lasalocid/day grew fastest and most efficiently and had the highest plasma glucose concentrations. Cattle fed monensin had rumen (P<.005) and plasma (P<.10) acetate to propionate ratios lower than the average of cattle fed any of the lasalocid supplements. Rumen (P<.005) and plasma (P<.10) acetate to propionate ratios increased from day 22 to day 79 of the 98-day experiment. Acetate and propionate concentrations were correlated (P<.05). Growth rate was correlated (P<.01) with feed consumption and feed efficiency. Acetate and propionate concentrations were not correlated with plasma glucose, and no metabolite concentrations were correlated with growth or feed efficiency.

Individual growth and feed intake of 36 Angus, 27 Polled Hereford and 30 Holstein steers were determined from 365 to 560 kg live weight. One-half of the cattle in each breed were fed a diet based on high-moisture ear corn and the other one-half were fed a diet based on corn silage. Within each breed × diet group, half of the cattle were implanted with zeranol. Cattle fed the high-moisture ear corn diet were 8% more (P<.01) efficient than cattle fed the corn silage diet. Cattle implanted with zeranol consumed 9% more (P<.005) dry matter and gained 15% (P<.005) faster, resulting in 5% (P<.05) less dry matter per unit gain than unimplanted cattle. Holstein steers gained 11% faster (P<.005) and consumed 8% less (P<.025) dry matter per unit gain than the average of Angus and Polled Hereford steers. Within subclass coefficients of variation were 9.9, 14.3 and 13.7 for daily dry matter intake, average daily gain and dry matter per unit gain, respectively; within subclass correlations were .50 (P<.01), .17 and −.75 (P<.01) between daily dry matter intake and average daily gain, daily dry matter intake and dry matter per unit gain and average daily gain and dry matter per unit gain. When combined with previous data that show Holsteins attain the Choice grade with less trimmable fat and equal weight of trimmed primal cuts compared with traditional beef breeds of the same live weight, these results suggest that Holstein steers are under-valued feedlot beef cattle.

The effect of live or carcass weight on yield of primal cuts, trimmed primal cuts, trimmed boneless primal cuts and primal cut fat trim was quantified in carcasses from 74 small-framed Angus and 71 Holstein steers. Animals were slaughtered at five within-breed weights. Primal cuts increased (P<.005) .44 kg and trimmed primal cuts increased (P<.005) .4 kg for each kg increase in shrunk body weight. One kilogram increase in shrunk body weight resulted (P<.005) in .37 kg of additional trimmed boneless primal cuts. The shrunk body weight of Angus steers and grain-fed cattle contained 4.28 (P<.01) and 9.32 (P<.005) kg more trimmed boneless primal cuts than their respective breed and diet counterparts. Each additional kg of chilled carcass weight resulted (P<.005) in .60, .13 and .50 kg of additional primal cuts, primal cut fat trim and trimmed boneless primal cuts, respectively. Neither diet nor housing type influenced the yield from chilled carcass weight. Breed differences in trimmed primal cut weight depended upon carcass weight. Holstein carcasses contained 9.1 and 15.5 kg more trimmed primal cuts at chilled carcass weights of 250 and 360 kg, respectively. Fat thickness and percentage kidney, pelvic and heart fat (KPHF) were the best (r2=.70) combination of predictors for percentage primal cuts. The best (r2=.77) combination of predictors for percentage trimmed primal cuts included chilled carcass weight as well as the best predictors for percentage primal cuts. Across diet and housing types, shrunk body weight explained between 89 and 98% and chilled carcass weight explained between 93 and 98% of the within-breed variation in weight of primal cuts processed to different stages.

The effects of live weight on carcass weight and of carcass weight on carcass characteristics were quantified using 145 large and small cattle represented by Holstein and small-framed Angus steers. Cattle were fed to one of five final weights ranging from 363 to 544 kg for Angus and from 454 to 612 kg for Holstein. Hot carcass weight increased (P<.005) .74 kg for each kg increase in live weight. Marbling score, quality grade and rib eye area increased (P<.005) .028 units, .027 units and .1 cm2, respectively, for each kg increase in chilled carcass weight. Angus carcasses had greater fat thickness and higher estimated percentage kidney, pelvic and heart fat (KPHF) except at heavier weights where percentage KPHF was greater for Holstein carcasses. Fat thickness increased .005 cm/kg faster (P<.005) and percentage KPHF increased .005 percentage units/kg slower (P<.025) for Angus carcasses. The only diet effect on carcass characteristics was a one-sixth quality grade difference (P<.05) in favor of the grain diet. Carcasses from all diets, breeds and housing types exhibited the same .012-unit change (P<.005) in numerical yield grade for each kg increase in chilled carcass weight. These results, combined with analyses of data from the literature, can be used to predict change in carcass weight with increasing live weight and changes in carcass characteristics with increasing carcass weight.

Growth and feed efficiency data were obtained on 146 large and small cattle represented by Holstein and small-framed Angus steers in a serial final weight experiment. Cattle were fed a grain- or silage-based diet in a low maintenance (inside) or a high maintenance (outside) environment. Steers were fed to one of five final weights ranging from 341 to 522 kg for Angus and from 431 to 612 kg for Holsteins. Daily dry matter intake (DDMI) was .67 kg greater (P<.005) for silage-fed than for grain-fed cattle and greater for Holstein than Angus steers. At comparable weights, Holsteins ate .76 kg more (P<.005) dry matter than Angus steers. Weight was a poor predictor of DDMI over these weight ranges, accounting only for 2 to 19% of the variation. Steers fed the grain diet gained .12 kg/day more (P<.001) than silage-fed steers. At comparable weights, Holsteins gained .2 kg/day more (P<.005) than Angus. Dry matter required per unit of gain (DM/G) was 1.79 units greater (P<.005) for silage-fed than for grain-fed steers, and .84 units greater (P<.005) for cattle kept outside than for cattle kept inside. At comparable weights, the small-framed Angus steers required 1 unit more DM/G than Holstein steers. Changes in DDMI, average daily gain (ADG) and DM/G with increasing weight did not differ between cattle of the two mature sizes. ADG declined by .18 kg/day and DM/G increased by 2.2 kg DM/kg gain with each 100-kg increase in body weight. Therefore, different equations for different mature size cattle may not be necessary to predict declines in ADG and feed efficiency associated with increasing weight.

The 9th–10th–llth rib sections from one side of each of 37 small-framed Angus and 34 Holstein steers slaughtered at five weights within breed were dissected into muscle, fat and bone. One-half of the steers of each breed were fed ad libituma high corn grain diet; the other half were fed ad libituman all-corn silage diet. One-half of the animals in each breed-diet group were housed conventionally, and half were housed in a warmer environment with movement restricted to individual pens. When rib weight was used as a covariate, analyses showed that Holstein steers had more (P<.005) muscle, less (P<.005) fat and more (P<.005) bone than Angus steers. At the same rib weight, grain-fed cattle had .12 kg more (P<.05) fat and .04 kg less (P<.05) bone than silage-fed cattle. Muscle content was not significantly affected by diet. While location did not affect tissue deposition in Holstein steers, Angus housed in the individual pens deposited more (P<.05) fat and less (P<.05) muscle in a given weight of rib than Angus steers housed conventionally. At the same ribeye area, Holsteins had more (P<.005) dissectable muscle than Angus, indicating that the longissimusmuscle is longer with a smaller diameter in Holstein than in Angus steers. Although at a given weight of rib, muscle to bone ratios were higher (P<.005) for Angus than for Holstein steers, analyses of covariance using bone as a covariate and a plot of muscle against bone showed that Angus and Holstein muscle data were part of the same (P>.10) population. Thus, differences in cattle shape were not reflected by different amounts of muscle at the same weight of bone. Use of muscle to bone ratio would have led to the incorrect conclusion that Angus have more muscle at the same weight of bone. Therefore, regression of muscle on bone is both biologically and statistically more satisfactory for interpretation of muscle growth and development patterns in cattle.

Rations composed of 0, 20, 40, 60 and 80% concentrate with the remainder being early (June 3) or late (July 7) cut mixed grass hay were fed to steers in a latin square design (five periods and five steers for each cutting date). Digestibility of ration dry matter was determined at the maintenance level of intake by total collection and by using acid insoluble ash (AIA) or permanganate lignin as indicators.Average rates of recovery of indicators were: permanganate lignin, 52.21 ± 1.79 and 59.25 ± 1.77%, and AIA, 101.19 ± 4.81 and 98.87 ± 2.98% for the early and late cutting dates, respectively. The permanganate lignin method underestimated digestibility determined by the total collection method by an average of 23.9 percentage units (P<.001). Thus, permanganate lignin is unreliable as an indicator in the ratio technique of measuring digestibility.When acid insoluble ash was used as an indicator, deviations from actual digestibility ranged from −3.62 (80% concentrate, late cut hay) to + 1.40 (40% concentrate, late cut hay) percentage units. The ration × method of determination interaction was not significant and the average deviation of -.62 was not significantly different from zero. Thus, digestibility by cattle of rations composed of hay and grain may be determined with AIA if a representative sample of feces is used.

An experiment was conducted to determine if dietary zinc at 100 or 500 ppm and copper at 8 or 125 ppm would affect growth, tissue Cu and Zn or plasma and liver cholesterol.Yorkshire pigs 6 to 8 weeks old were fed a practical corn-soybean meal diet incorporating a 2× 2 factorial treatment arrangement of zinc and copper. The experiment began shortly after weaning and continued until the animals reached slaughter weight. Blood samples were obtained at 0, 2, 4, 8, 12 and 16 weeks (slaughter) of the experiment for determination of plasma Zn, Cu and cholesterol concentrations. Liver and kidneys were removed at slaughter for Zn, Cu and cholesterol (liver only) concentrations. Samples of several tissues were saved for histopathologic examination.Liver and kidney Zn and Cu concentrations reflected dietary Zn and Cu. Plasma Zn also reflected levels fed throughout the experimentalperiod. In contrast, plasma Cu was not altered by diet.Plasma cholesterol was significantly higher in animals fed the two high Zn diets after 4 weeks of treatment; however, Cu-supplemented animals manifested decreased plasma cholesterol compared to their respective Zn counterparts. Both effects dissipated with time. After 12 weeks of treatment, both a Cu× Zn and Zn× sex interaction were evident. There was no significant difference in liver cholesterol among dietary treatments and no evidence of tissue atherosclerotic lesions in any of the pigs. It is concluded that there is no evidence for a biologically significant influence of dietary Zn or Cu, at the levels used here, on plasma or liver cholesterol concentrations in the pig.

The use of W.75as an estimator of fasting heat production (HP) for male and female rats, chickens, rabbits, dogs, humans, cattle and for ewes was studied using data obtained from the literature. Regression coefficients for models which related HP to body weight (W) were calculated from data for each population of animals. Highly significant (P<.001) equations were obtained for animals in each species-sex subclass, thus nullifying the common assumption that the narrow W ranges within species prevent the determination of meaningful relationships between HP and weight.Data from various sources within species-sex subclasses did not differ with respect to b1for the model: log HP = b0+ b1(log W). However, source of data did affect b0for dogs, ewes, women and steers. Weight exponents (b1values) were significantly different for the sexes within the chicken, dog, and human species.Tests for equality of weight exponents showed that exponents derived for species-sex-source, sex-source within species, and species-source within sex subclasses were not equal (P<.001). Thus, a universal equation which relates HP to W should not be declared the best fitting equation for species-sex subclasses. It is concluded that W.75, which was developed from data of species varying widely in W, ignores effects other than weight which are peculiar to specific populations. Therefore many researchers have inappropriately adjusted biological data for variation in weight by dividing response criteria by W.75. A more appropriate adjustment would be to include Wbor log W as a covariable in the statistical model.

Boneless rib eye steaks from 32 Holstein and 32 Simmental × Angus steers were evaluated by 55 supermarket meat managers. Within breed, steers were divided into light or heavy initial weights. Within initial weight groups, steers were either implanted with Revalor or not implanted. Steers were slaughtered commercially when they reached a small degree of marbling, and rib eye steaks were cut from the carcass and stored at −20°C until the day before evaluation. After thawing overnight in a 0 to 4°C cooler, uncooked steaks were randomly assigned to positions on paper plates. Each of the 55 evaluators was then told to record whether each steak was from a Holstein or a traditional beef breed. The percentage identified correctly was 50.9 ± .96, which was not different from being random. Steaks were later assigned to blocks of eight treatments and cooked to an internal temperature of 68*C before six or seven participants evaluated steaks from each block. Sensory attributes were acceptable for all steaks. Steaks from Holstein steers generally were superior to those from Simmental × Angus steers. Steaks from steers with heavy initial weights generally were superior to steaks from steers with light initial weights. Steaks from steers implanted with Revalor were slightly less acceptable than steaks from unimplanted steers for several sensory attributes, but the difference in overall acceptability was minor and nonsignificant. All the differences were small, and may have limited commercial relevance.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of bovine growth hormone (GH) and thyroxine (T4) on growth and carcass characteristics were assessed in Dorset ram lambs. Lambs in four groups (n = 10/group) were treated for 30 d as follows: controls, 3.33 mg (6 IU) GH/d (s.c.); 5-mg T4implant (s.c.) on d 1 and a 10-mg T4implant 21 d later; GH + T4. Blood samples were collected at 3-d intervals for analysis of GH, T4, triiodothyronine, somatomedin-C and testosterone concentrations. Six lambs/group were slaughtered for carcass measurements and composition. Daily GH injections increased (P< .005) baseline plasma GH levels 10-fold, whereas plasma T4concentrations were increased 10% (P< .10) by the implants. Somatomedin-C increased with time in all groups, but the increments from d 0 to d 30 were higher (P< .05) with GH treatment. Average daily gain (mean = 352 g/d), feed consumption and feed to gain ratio were not affected (P> .1) by GH or T4treatment in ram lambs. Hot carcass weight and dressing percentage were increased (P< .05) by T4. Growth hormone increased carcass protein content (P< .005) and muscle weights while reducing carcass fat (P< .05). Carcass composition was not altered by T4alone, and the T4× GH interaction was not significant; however, the combination of T4and GH resulted in greater muscle and protein weight than did either hormone alone or no hormone administration. There were no differences in bone length or in the metacarpal growth plate width among groups. The beneficial effects of GH on carcass composition were not further enhanced by administration of thyroxine.

The objective was to study control of mature size by characterizing metacarpal growth plate closure in relation to relevant bone growth-regulating hormones in two breeds exhibiting distinct differences in mature frame size. Thirty-four Suffolk and 34 Dorset ram lambs were slaughtered in pairs within breed at birth, weaning and monthly intervals until 420 d and then bimonthly to 600 d. Plasma growth hormone was depressed to undetectable levels due to the high-energy, ad libitum-fed diet. Plasma insulin-like growth factor-I (IGF-I) rose over the growth period from 116 ng/ml (newborn Suffolk) to a high of 451 ng/ml (420-d Dorset); it appeared to peak at approximately 400 d and then declined to a stable level. Dorsets consistently exhibited higher IGF-I levels. The thyroid hormones exhibited no apparent age association. An age-associated rise was detected for testosterone, but not for estradiol. Mature metacarpal lengths were estimated to be 147.2 and 127.4 mm for Suffolks and Dorsets, respectively. Ninety-five percent of mature length was attained in Suffolks by 226 d and in Dorsets by 165 d. Growth plates, however, did not begin to appear closed until 390 d and closure was not complete in all animals until 480 d, suggesting that metacarpal growth rate was dissociated temporally from growth plate closure. Although growth plate closure likely is controlled by the endocrine system, there were no apparent relationships between circulating hormones and growth plate width, age at closure or zonal divisions within the growth plate, suggesting that the growth plate experiences a very different hormonal environment than what can be measured in the circulating blood.

Chopped hay supplemented with a volatile fatty acid salt mixture at 20% of metabolizable energy (ME) was fed to 30 Suffolk × Corriedale lambs (mean wt 29.6 kg) to determine the effects of dietary propionate on weight gain, body composition and plasma metabolites. Propionate accounted for 0, 25, 50, 75 or 100% of the salt mixture energy, and acetate accounted for the remainder. Each diet was fed at two levels of daily intake (158.7 and 130.6 kcal ME/W.75). Lambs on the high level of intake lost more (P< .05) energy in feces, lost less (P< .05) energy in CH4and had carcasses with more (P< .10) water and fat than lambs on the low intake level. Percentage of propionate in the salt mixture had no effect on ME or body composition of lambs. Increasing the percentage of propionate in the salt mixture increased plasma propionate in blood samples taken at 1 and 2 h after feeding (linear, P< .05). Empty body weight gain per megacalorie of ME above maintenance increased as the percentage of propionate in the salt mixture increased, but not until propionate reached 75% of the salt mixture (linear, P< .05; cubic, P< .05). These results show that propionate in the blood has a positive, but nonlinear, effect on weight gain, even when energy intake is held constant.

Exogenous sex steroids have altered growth hormone secretion in some domestic species. This study examined whether different physiological concentrations of testosterone alter muscle growth in sheep through modification of the somatotropic axis. The effects of testosterone on growth hormone (GH), insulin-like growth factor-I (IGF-I), estradiol (E2) and cortisol concentrations in growing lambs were evaluated in 20 rams, 20 wethers and 20 wethers receiving subcutaneous testosterone replacement therapy. Two animals from each of the three testosterone status groups were slaughtered at 14-day intervals from 49 to 133 days of age, and then at 28-day intervals until 217 days of age for a total of 10 slaughter ages. Animals were sampled every 10 min for an 8-h period 1 day prior to slaughter to characterize the episodic patterns of GH and testosterone. Immediately after slaughter, the semitendinosus, splenius and triceps brachii muscles were removed, trimmed of adhering fat and connective tissue, and weighed. Testosterone increased the combined muscle weight. GH concentrations decreased during the course of the experiment. However, there was no effect of testosterone on GH mean, baseline, amplitude or GH pulse frequency measured by PULSAR. IGF-I concentrations increased in response to testosterone treatment. Testosterone had no effect on cortisol levels while E2levels were increased after 133 days. Increased muscle growth due to testosterone appeared to be caused either by a direct effect or by increased levels of IGF-I independent of circulating GH concentrations.Journal of Endocrinology(1996) 150,391–399

Seventy-four small-framed Angus and sixty-nine Holsteins were used to evaluate the classic Hankins and Howe equations for predicting percentages of water, protein, and lipid of steer carcasses varying in weight and breed type. Animals were fed either corn grain or corn silage diets, housed inside or outside, and slaughtered at one of five predetermined weights within breed. Soft tissues from a carcass side and the from the 9-10-11th rib section were separated from bone, and the percentages of water, protein, and lipid were measured. The Hankins and Howe equations predicted .81 ± .181 percentage units more (P< .001) water and .99 ± .213 percentage units less (P< .001) lipid than was measured in the carcasses. The residual difference for protein depended on breed and diet (P< .028) and decreased .22 ± .078 percentage units for each percentage unit increase in predicted protein. During development of equations from our data, no statistical difference was found between Angus and Holstein in the relationship of carcass water to rib water. The relationship of carcass protein to rib protein had a lower (P< . 1 ) intercept with a steeper (P< .055) slope for Angus than for Holstein steers, whereas for lipid there was no difference between the slopes, but Holsteins had one percentage unit more (P< .038) carcass lipid than Angus at the same percentage rib lipid. These results confirm that composition of the 9-10-11th rib section can be used accurately to predict carcass composition with minor adjustments for breed type.

Sheep are one of the few livestock species that are seasonally polyestrous therefore limiting lamb production to specific times of the year. However there are certain breeds, such as the Dorset and Polypay, which have been selected for the ability to lamb outside the traditional spring lambing period. Even within these breeds there is substantial variation in the ability of an ewe to lamb out of season in the U.S. Out of season lambing has a low estimated heritability of 0.08. Trait expression generally requires multiple years of breeding to determine both reproductive success and out of season success. Lastly, it is only expressed in females. These properties make selection progress difficult to achieve based on phenotype alone. For this study, Dorset and Dorset × Finn ewes were classified as Seasonal (controls) or Aseasonal (cases) based on their historical out of season breeding success. Success was defined as the percentage of times an ewe lambed divided by the number of times she was exposed to a ram. Seasonal success applied to lambings occurring from January through May while Aseasonal success applied to lambings occurring from August to November. All ewes had a seasonal reproductive success rate of 66% ensuring that overall reproductive success was not a limiting factor for Aseasonal potential. All ewes were exposed for out of season breeding at least 3 times. Ewes were defined as Aseasonal if their out of season lambing success rate was greater than 65%. Seasonal ewes were defined as ewes with an out of season lambing success rate less than 35%. Individuals were genotyped using the Illumina Ovine Infinium HD SNP BeadChip providing 606,006 SNP markers spanning the genome for analysis. Fifty-four Individuals (26 cases and 28 controls) and 478,494 SNPs passed quality control measures for use in a genome-wide association study. The most significant SNPs (FDR p< 0.05) were discovered using EMMAX to correct for population stratification and a dominant inheritance model. These SNPs are located on chromosomes X, 25, 7, and 4. Potential candidate genes include NREP,involved with neuron function, LRRN3,involved with synapse assembly, and IMMP2L,involved with follicular development. This study provides preliminary data which is being followed up with additional Dorset and Polypay sheep for validation. It is the first step toward identifying major genes responsible for out of season lambing sheep and developing markers to assist selection.