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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.

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.

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.