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Apoptosis is a form of cell death that involves the changes of mitochondrial function and the regulated activation of caspase cascades, which selectively cleave cytoskeleton proteins and catalyze the changes of cell organelles and morphological structure. The changes of mitochondrial function, cell morphological structure, and degradation of cytoskeleton are considered to be responsible for the development of meat qualities. The LM, semitendinosus, and psoas minor (PM) muscles of 5 crossbred bulls were used to observe the morphologic and quantitative changes of apoptosis, as well as the change of caspase-3 activity during 7 d storage. Transmission electron microscopy shows that the typical features of apoptosis appeared in muscles between d 1 and 4. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) positive nuclei were detected at d 4 and increased subsequently. The count of TUNEL-positive nuclei was different in 3 muscles at d 7 (P < 0.001). There was a significant increase in caspase-3 activities at 4 h postmortem relative to the activities at the first 30 min in 3 muscles (P = 0.0147 in LM; P = 0.0058 in PM; P = 0.0306 in semitendinosus), and the apexes had 2.9 to 6.5 times more activities than activities at the first 30 min postmortem. Apoptosis did exist in 3 types of muscles during the conditioning period. Apoptosis and caspase cascades system could be associated with the postmortem development of meat quality in skeletal muscles of bulls. Key words: apoptosis, caspase-3, conditioning, postmortem, skeletal muscle doi: 10.2527/jas.2009-2412

The effects of low-protein (LP) diets and tureen-protected CLA on DMI, ADG, carcass traits, and health status of double-muscled Piemontese young bulls were investigated. Forty-eight bull calves (BW = 237 [+ or -] 24 kg) were divided in 4 groups and housed in 12 fully slatted pens. Bulls were fed 2 diets differing in CP density [high-protein (HP) diet: CP = 145 g/kg of DM; LP diet: CP = 108 g/kg of DM] and top-dressed with 80 g/d of rumen-protected CLA or 65 g/d of hydrogenated soybean oil. Orts were collected weekly and feed intake was estimated on a pen basis, with 3 replicated pens for each treatment. Each bull was weighed monthly and examined for alterations of the locomotion system by using the locomotion score as an index of lameness and by counting the number of swollen joints. Carcass quality traits were measured at slaughter, after a feeding period of 332 d. Compared with HP, LP reduced ADG only during the first 4 mo of the trial (1.30 vs. 1.53 kg/d, P = 0.003). However, be cause of compensatory growth, over the whole trial, no significant effects attributable to CP or to additive were found on final BW (668 kg), ADG (1.19 kg/d), DMI (8.50 or 86 g/d per kg of [BW.sup.0.75]), dressing percentage (67.3%), carcass conformation (5.2 points), and carcass fat covering (1.87 points). Feed efficiency was affected by a CP x additive interaction (P = 0.030), with CLA improving feed efficiency when added to the LP diets, whereas feed efficiency was reduced with the HP diets. The addition of both LP and CLA reduced the number of bulls presenting swollen joints (P = 0.001), and LP improved the locomotion score (P = 0.021) compared with HP. It was concluded that 10.8 g/kg of CP density in the diet is sufficient for double-muscled Piemontese bulls. The reduction in CP density from 145 to 108 g/ kg of DM, in addition to reducing the feeding cost, allows a strong reduction in N consumption without negative consequences on growth performance and carcass traits. Key words: conjugated linoleic acid, double-muscling, lameness, locomotion score, Piedmontese breed, protein requirement doi: 10.2527/jas.2009-2558

Previous research suggests that the digital cushion, a shock-absorbing structure in the claw, plays an important role in protecting cattle from lameness. This study aimed to assess the degree to which nutritional factors influence the composition of the digital cushion. This involved quantifying lipid content and fatty acid composition differences in digital cushion tissue from cattle offered diets with different amounts of linseed. Forty-six bulls were allocated to 1 of 4 treatments, which were applied for an average of 140 [+ or -] 27 d during the finishing period. The treatments consisted of a linseed supplement offered once daily on top of the basal diet (grass silage:concentrate) at 0, 400, 800, or 1,200 g of supplement/animal per day. For each treatment, the concentrate offered was adjusted to ensure that total estimated ME intake was constant across treatments. Target BW at slaughter was 540 kg. Legs were collected in 3 batches after 120, 147 and 185 d on experiment. Six samples of the digital cushion were dissected from the right lateral hind claw of each animal. Lipids were extracted and expressed as a proportion of fresh tissue, and fatty acid composition of the digital cushion was determined by gas chromatography. Data were analyzed by ANOVA, with diet, location within the digital cushion, and their interactions as fixed effects and fat content (grams per 100 g of tissue) as a covariate. Linear or quadratic contrasts were examined. The lipid content of digital cushion tissue differed between sampling locations (P < 0.001) but did not vary by treatment. There were quadratic responses to increasing linseed supplementation for several fatty acids. Although the overall proportion of C18:3n-3 (the most abundant fatty acid in linseed) did not differ (P < 0.33) by treatment, there was a quadratic influence of diet on total PUFA concentration (P = 0.003) and a linear increase in C18:3n-3 as a proportion of total PUFA (P = 0.01) in the digital cushion. This work demonstrates that dietary fatty acid composition influences the concentration of fatty acids incorporated in the digital cushion of cattle. Based on the large number of quadratic responses among the fatty acids, it appears there is a threshold amount of fatty acid incorporation in the digital cushion. Key words: digital cushion, fatty acid, linseed, lipid, n-3 fatty acid doi: 10.2527/jas.2009-1972

The objectives of this study were to analyze body measurements of 40 crossbred bulls grazing low quality forage with different supplementation strategies, to estimate interrelationships among those measurements and carcass and body compositions, and to develop systems of equations to predict body fat using body and carcass measurements. Eight animals were slaughtered at the beginning of the experiment, and the remaining animals were slaughtered at 90 or 220 d. The biometric measures (BM) were obtained the day before the slaughter and included hook width, pin width, pelvic girdle length, rump depth, rump height, abdomen width, body length, height at withers, rib depth, girth, and body diagonal length. Other measurements included full, shrunk, and empty BW; internal physical and chemical fats; body volume; body area; carcass weight; 9th-to 11th-rib section weight and composition; fat thickness; subcutaneous fat; intermuscular fat; carcass chemical fat; and empty body physical and chemical fats. The relationships between BM and body components were evaluated, and equations to predict body area, body volume, subcutaneous fat, and carcass and body physical and chemical fat were developed. Biological interpretations of the parameter estimates of equations were similar to those found in the literature such as a ratio of 1 kg of subcutaneous fat to 1.6 kg of intermuscular fat and a deposit of 72 to 76% of body fat in the carcass. The first system used to predict carcass and empty body physical and chemical fat was devised using in vivo information, whereas the second system used BW and the 9th-to 11th-rib fat weight. Our results indicated the combination of BW, carcass traits, and BM was precise and accurate in estimating carcass and body fat composition of backgrounding bulls. The second system had better adequacy statistics [r.sup.2] > 0.92, concordance correlation coefficient (CCC) > 0.957, and root mean square error (RMSE) < 14.4% of the average observed value] compared with the first system. The first system had acceptable adequacy statistics ([r.sup.2] > 0.767, CCC > 0.866, and RMSE varying from 15.8 to 22.3% of the average observed value). For both systems, the simultaneous F-test of the linear regression of observed on model-predicted values indicated intercepts were equal to zero, and slopes were equal to 1 (P > 0.246). We concluded that BM can improve the accuracy and precision of the predictions of body composition of grazing animals. Key words: biometrics, cattle, composition, modeling, prediction, simulation doi: 10.2527/jas.2009-1919

The objective was to investigate measures of neutrophil function in response to banding or burdizzo castration of bulls. Thirty-two Holstein-Friesian bulls (14 mo old, 505 [+ or -] 7.8 kg of BW) were assigned to 1 of 4 treatment groups: 1) sham-handled control (CON); 2) banding castration alone (BAND); 3) burdizzo castration alone (BURD); or 4) cortisol infusion (CORT) as a further control group. For each group on d -14, 8 animals (2 animals/treatment) were tied up in tie stalls (day of treatment = d 0). At -2, 2, 6, 12, 24, 48, 72, and 144 h relative to treatment time, blood samples were collected for analyses of neutrophil phagocytosis and respiratory burst, neutrophil CD62-L expression, and serum IL-8 concentration. Leukocyte counts, phagocytosis activity, and CD62-L expression were similar (P > 0.05) among the 4 treatment groups. The BURD castrates had greater burst activity compared with BAND castrates (P = 0.048) and CON (P = 0.01) at 72 h posttreatment. The BURD castrates had a greater percentage of granulocyte positive leukocytes (Gr%; P < 0.01) at 2 h posttreatment compared with CON and CORT bulls. The BURD castrates had greater (P < 0.05) Gr% compared with BAND, CON, and CORT animals at 24, 48, and 72 h posttreatment. The BURD and BAND castrates had greater Gr% (P < 0.05) compared with CORT bulls at 144 h posttreatment. In general, BAND, BURD, and CORT did not affect serum IL-8 concentration. Banding castration, BURD, and CORT did not induce leukocytosis, whereas BURD induced a modest neutrophilia. Neutrophil functioning in terms of phagocytosis and respiratory burst and serum IL-8 concentration were not compromised by BAND, BURD, and CORT. These findings indicate nonsurgical castration is unlikely to induce a severe acute systemic inflammatory response in terms of neutrophil function. Key words: castration, cattle, CD62-L, interleukin-8, phagocytosis, respiratory burst

The present study aimed to evaluate the effects of rearing system and level of dietary protein supplementation on growth performance, metabolic profile, plasma leptin, and carcass composition of young Podolian bulls. At the beginning of the finishing period (about 14 mo of age), animals were divided into 3 groups according to rearing system and dietary protein level: indoor receiving a diet with 15% CP of DM (IND); and outdoor, at pasture, receiving a supplementation with 12% CP of DM (OUT12) or with 15% CP of DM (OUT15). Plasma leptin concentration increased (P < 0.05) with age, whereas it was unaffected by rearing system and protein level. Positive correlations between plasma leptin concentration, ADG (r = 0.861, P < 0.001), and blood glucose concentration (r = 0.977, P < 0.001) were observed, whereas NEFA and triglycerides were not correlated with leptin concentration. At the end of the finishing period (about 20 mo of age), young bulls in the OUT12 group showed greater (P < 0.05) cholesterol concentrations in blood than the OUT15 group, whereas the OUT15 group showed greater urea concentrations compared with IND (P < 0.01) and OUT12 groups (P < 0.001). Average daily gains, feed conversion ratio, and final BW were similar between groups. Intramuscular lipid content of LM, semitendinosus, and semimembranosus muscles was correlated with plasma leptin before slaughtering (r = 0.77, P < 0.01; r = 0.67, P < 0.01, r = 0.79, respectively). Correlations between plasma leptin and intramuscular fat were found starting from 18 mo of age for LM (r = 0.44; P < 0.05) and from 19 mo for semimembranosus (r = 0.56; P < 0.05) and semitendinosus (r = 0.58; P < 0.05). Mean value of intramuscular fat and intramuscular fat of LM was greater in OUT15 than OUT12 (P < 0.05). No differences were found between 12 and 15% CP supplementations for growth and carcass data. Therefore, we conclude that the extensive rearing system supplemented with 12% CP may be adequate to sustain good growth performance and carcass quality from the Podolian breed. These data also provide confirmation that leptin, in cattle, is directly related to nutritional status and may represent a suitable predictor for body fat starting from 1 mo before slaughtering. Key words: carcass composition, leptin, metabolic profile, Podolian cattle, protein level, rearing system

Forty-eight bulls (335 [+ or -] 8.6 kg of initial BW) were randomly assigned to 4 glycerin levels (0, 4, 8, and 12% of concentrate DM) with the objective of evaluating the effects of glycerin supplementation on performance, ruminal fermentation, metabolism, and carcass and meat quality in Holstein bulls fed high-concentrate diets. Concentrates were formulated to be isonitrogenous and isocaloric (assuming a glycerin ME content of 3.47 Mcal/kg of DM). Concentrate and straw were fed for ad libitum intake. Bull BW and feed consumption were recorded monthly. Additionally, rumen and blood samples were collected every month. Bulls were slaughtered after 91 d of study (460 [+ or -] 11 kg of final BW). Hot carcass weight, carcass backfat, and conformation were recorded. The area, Warner-Bratzler shear force, and intramuscular fat content of LM were determined. Glycerin level did not affect daily concentrate intake (6.89 [+ or -] 0.34 kg/d of DM), straw intake (1.38 [+ or -] 0.069 kg/d of DM), total DMI (8.27 [+ or -] 0.32 kg/d of DM), ADG (1.36 [+ or -] 0.087 kg/d), or G:F (0.17 [+ or -] 0.009). Similarly, rumen molar proportions of propionic, acetic, and butyric acids, and rumen liquid osmolality were unaffected by treatment. However, a decreased rumen pH (P < 0.05), and greater rumen total VFA concentration (P = 0.09), serum insulin concentration (P < 0.05), and insulin to glucose ratio (P < 0.05) were observed in bulls fed 8% glycerin in concentrate compared with those receiving 0, 4, or 12%. No changes were observed in carcass and meat quality. The ME content of glycerin (86% glycerol) can be assumed to be 3.47 Mcal/kg of DM in Holstein bulls fed high-concentrate diets. In addition, feeding concentrate containing up to 12.1% of glycerin does not lead to detrimental effects on performance, ruminal fermentation, metabolism, and carcass and meat quality variables. Key words: beef, glycerol, meat, rumen

A meta-analysis was conducted to determine NE and net protein requirements of growing bulls, steers, and heifers of Nellore purebred and Nellore x Bos taurus crossbreds. A database of 16 comparative slaughter studies (n = 389 animals) was gathered to provide enough information to develop equations to predict the requirements of [NE.sub.m], [NE.sub.g], and net protein for maintenance ([NP.sub.m]) and growth ([NP.sub.g]). The data were analyzed using a random coefficients model, considering studies as random effects, and sex and castrate status (bulls, steers, and heifers; n = 262, 103, and 24, respectively) and breeds as fixed effects. There were no differences in [NE.sub.m] requirements among sex and castrate status (P = 0.73) and breeds (P = 0.82). The combined data indicated a [NE.sub.m] requirement of 75 kcal/ [kg.sup.0.75] of empty BW (EBW) with a partial efficiency of use of ME for [NE.sub.m] of 0.67. The [NE.sub.g] requirement was different (P = 0.009) among sex and castrate status and tended (P = 0.06) to be different among breeds. The equation for [NE.sub.g] requirement for bulls was 0.0514 x [EBW.sup.0.75] x [EWG.sup.1.070]; for steers, it was 0.0700 x [EBW.sup.0.75] x [EWG.sup.1.070]; and for heifers, it was 0.0771 x [EBW.sup.0.75] x [EWG.sup.1.070], where EWG = EBW gain (kg/d). The partial efficiency of use of ME for [NE.sub.g] was not different among sex and castrate status (P = 0.33) and breeds (P = 0.20) and averaged 0.44. There were no differences in [NP.sub.m] requirement among sex and castrate status (P = 0.59) and breeds (P = 0.92); the overall [NP.sub.m] requirement was 1.74 g of NP x [kg.sup.-0.75] of EBW x [d.sup.-1]. The overall MP requirement for maintenance was 2.59 g of MP x [kg.sup.-0.75] EBW x [d.sup.-1]. The [NP.sub.g] requirement (g/d) was not different among sex and castrate status (P = 0.59) and breeds (P = 0.14); the overall equation was EWG x [217 - (12.8 x RE/EWG)], where RE = retained energy (Mcal/d). The percentage of RE deposited as protein (%[RE.sub.p]) decreased exponentially as the content of RE in the gain (REc, Mcal/kg of EWG) increased. Because no study effect was observed, we pooled the data across studies and the overall equation to predict %[RE.sub.p] was 10.1 + [167e.sup.(-0.66 x REc)]. Our results do not support the hypothesis that bulls have greater [NE.sub.m] requirements than steers and heifers. Likewise, no significant differences in the [NP.sub.m] requirements among bulls, steers, and heifers were detected. Nonetheless, the [NE.sub.g] requirement of steers was greater than bulls and less than heifers. Even though the %[RE.sub.p] was negatively correlated with the concentration of energy in the EWG, our findings indicated no differences in [NP.sub.g] requirement among bulls, steers, and heifers. Key words: Bos indicus, comparative slaughter, growth, Nellore, net energy, net protein

Transportation causes stress in cattle that may alter numerous physiological variables with a negative impact on production and health. The objectives of the current study were to investigate the physiological effects of truck transportation and to characterize a pattern of phenotypes in the circulation that may aid in the early identification of stress-susceptible animals that often succumb to severe respiratory disease. Thirty-six young beef bulls (Aberdeen Angus, n = 12; Friesian, n = 12; and Belgian Blue x Friesian, n = 12) were subjected to a 9-h truck transportation by road. Blood (10 mL) was collected at -24, 0, 4.5, 9.75, 14.25, 24, and 48 h relative to the initiation of transportation (0 h). Plasma was collected for the assay of various metabolic, inflammatory, and steroid variables, and total leukocyte counts were determined in whole blood at each time point. Body weight and rectal temperature were recorded at -24, 9.75, and 48 h. Transportation decreased measures of protein metabolism in the plasma, including albumin (P = 0.002), globulin (P < 0.001), urea (P = 0.006), and total protein (P < 0.001), and increased creatine kinase (P < 0.001). The energy substrate [beta-hydroxybutyrate was not changed (P = 0.27). Acute phase proteins haptoglobin and fibrinogen were both decreased (P < 0.001), whereas total leukocyte counts were elevated (P = 0.002). Circulating steroid concentrations were altered, because a classical acute increase in plasma cortisol was observed with the onset of transit (P < 0.001), in association with a decrease in dehydroepiandrosterone (P = 0.07), resulting in a profound increase in cortisol:dehydroepiandrosterone ratio (P < 0.001). Plasma testosterone was decreased, whereas plasma progesterone was increased (P < 0.001) in association with the increase in cortisol (P < 0.001). There was also an effect of breed for all variables except plasma urea, creatine kinase, and testosterone, perhaps indicating that a genetic component contributed to the physiological response to transportation stress, although without any clear trend. Taken together, this profile of physiological variables in the circulation of transportation-stressed bulls may aid in the future detection of disease-susceptible cattle after transportation. Further research to validate these potential biomarkers is necessary. Key words: beef cattle, biomarker, disease, physiology, plasma, transportation stress

Economic benefits from the use of expected progeny of a sample of beef bulls with genetic evaluations were calculated over an integrated supply chain for combinations of price discounts for intramuscular fat and LM area. Fixed backfat finish and marketing at the point of optimized gross margins were considered. An economic model was used to calculate average expected gross margins for a sample of bulls. Across-breed, age-constant genetic evaluations were used to predict carcass characteristics of progeny including weight, retail yield, intramuscular fat, and LM area, as well as input requirements including feed and housing as a function of time on feed. Proportion of retail cuts affected by price discounts was included in the calculations. Optimizing endpoints did not affect rankings to any extent relative to a fixed end point in this sample of bulls, as a result of fixed endpoints being similar to optimized endpoints for the economic situation considered. However, rank correlations were only 0.63 and 0.71 between rankings for no discount being applied and rankings with discounts for intramuscular fat and LM area, for fixed and optimized endpoints, respectively. We conclude that market prices are necessary considerations in choices of bulls to use in commercial beef production. Key words: beef production, bioeconomic model, genetic evaluation, sire ranking

The objectives of this study were 1) to compare temperament assessments, using multiple techniques and over repeated observations, to gauge temperament over the long-term and 2) to evaluate the relationship of the temperament appraisals with serum concentrations of cortisol (CS). Measures of temperament were gathered over 3 repeated observations (60-d interval) of yearling, fall-born Brahman bulls (initial BW = 320 [+ or -] 4 kg; n = 66). Temperament assessments included exit velocity (EV), which was the rate at which the bulls exited the squeeze chute and traversed a fixed distance (1.83 m); pen scores (PEN; 1 = quiet to 5 = excited), ascertained from animal behavior while penned in small groups (n = 5); and chute scores (CHUTE; 1 = quiet to 5 = excited), determined from behavioral responses to restraint on the weigh scale. Temperament measures obtained during the initial data collection (d 0) were all positively correlated (r [greater than or equal to] 0.35, P < 0.005) with one another. Additionally, PEN (r = 0.29, P < 0.05) and EV (r = 0.26, P < 0.05) were positively correlated with CS, whereas CHUTE was not (r = 0.09, P = 0.46). All serial EV measures were positively correlated (r > 0.31, P < 0.02). All PEN were positively correlated (r > 0.31, P < 0.01), whereas serial measures of CHUTE were not (P > 0.3). Exit velocity was positively correlated with CS within d 0 (r = 0.26, P = 0.04) and 120 (r = 0.44, P < 0.01). The EV data obtained at d 0 were transformed into a discrete variable, EV ranking (EV RANK; 1 to 3 scale), in which 1 equated to 1 SD above the mean. Mean EV (P < 0.01) decreased from d 0 (2.82 [+ or -] 0.07 m/sec) to 120 (2.11 [+ or -] 0.10 m/sec). Time also influenced (P < 0.01) CS; mean CS decreased between d 0 (14.6 [+ or -] 0.7 ng/mL) and 120 (11.1 [+ or -] 0.8 ng/ mL). Measures of EV can be a valuable tool for the assessment of cattle temperament and a possible predictor of temperament and stress responsiveness to future animal handling events. Key words: cattle, cortisol, exit velocity, temperament

The objective of the present study was to evaluate the secretion of testosterone (T) in bulls in response to the administration of varying doses of bovine LH (bLH) during the four seasons of the year. Five adult bulls (4 yr of age) were treated with an amount of bLH that was estimated to induce a 5 ng/mL amplitude pulse of LH in blood serum on five consecutive days around the spring equinox, summer solstice, fall equinox, and winter solstice. Five hours after this dose, bulls were treated with bLH in amounts that were estimated to induce a 0.25, 0.5, 1, 2, or 4 ng/mL amplitude LH pulse in blood serum in a Latin square design. Blood samples were collected for 5 h after administration of a dose of bLH that was estimated to induce the 5-ng amplitude LH pulse, and for 3 h after administration of the variable doses of bLH, and were then assayed for concentrations of T. Average concentrations and amplitude of T release after doses of bLH that were estimated to induce the 5-ng amplitude LH pulses were greater during the spring and summer than during the winter (P < 0.05). The area under the release curve (AUC) was greater during the spring than during the winter (P < 0.05). During the 3 h after treatment with the variable doses of bLH, T response was affected by dose (P < 0.001) and season (P < 0.001), but there was no dose x season interaction. Testosterone response increased in a dose-dependent fashion for all variables studied. The greatest average concentrations of T and AUC were observed in the spring compared with the fall and winter (P < 0.05). These data support our working hypothesis that testes of bulls are more responsive in releasing T in response to bLH stimulation in the spring and summer compared with the winter; however, there were no changes in sensitivity of the testes to LH during different seasons of the year as indicated by the lack of a dose of bLH x season interaction. Key Words: Cattle, Male Animals, Seasonal Variation, Testes, Testosterone

The objective of this study was to estimate genetic parameters for real-time ultrasound measurements of longissimus muscle area (LMA), 12th rib backfat thickness (FT), percent intramuscular fat (IMF), and yearling weight (YW) for 1,299 yearling Brangus bulls and heifers. A single ultrasound technician performed all measurements. The number of observations was 1,298, 1,298, 1,215, and 1,170 for LMA, FT, IMF, and YW, respectively. Genetic parameters were estimated for each trait using single- and multiple-trait derivative-free restricted maximal likelihood. Fixed effects were contemporary group (defined as same sex, same age within six months, and same environment), and days of age as a covariate. Correlations were estimated from two-trait models. Heritabilities for LMA, FT, IMF, and YW were 0.31, 0.26, 0.16, and 0.53, respectively. Genetic correlations between LMA and FT, LMA and IMF, LMA and YW, FT and IMF, FT and YW, and IMF and YW were 0.09, 0.25, 0.44, 0.36, 0.42, and 0.31, respectively. Yearling live animal ultrasonic measurements can be used as a selection tool in breeding cattle for the improvement of carcass traits. Key Words: Genetic Correlation, Genetic Parameters, Heritability, Ultrasound

Longissimus muscle area and fat thickness were measured following weaning, at yearling, and prior to harvest using real-time ultrasound, and corresponding carcass measurements were recorded 3 to 7 d following the preharvest scan in composite steers (n = 116, 447 [+ or -] 19 d), bulls (n = 224, 521 [+ or -] 11 d), and heifers (n = 257,532 [+ or -] 12 d). Although fat deposition was limited in bulls and heifers from weaning to yearling, coefficients of variation ranged from 8.46 to 13.46% for muscle area, and from 27.55 to 38.95% for fat thickness, indicating that significant phenotypic variance exists across genders. Residual correlations, adjusted for the effects of year of birth, gender, and age at measurement, were high and ranged from 0.79 to 0.87 among ultrasound and carcass measures of muscle area. Residual correlations among ultrasound and carcass measures of fat thickness were also high, ranging from 0.64 to 0.86. Weaning and/or yearling ultrasound muscle area yielded similarly accurate predictions of carcass muscle area. Yearling ultrasound fat thickness accounted for 13% more of the observed variance in carcass fat thickness than the weaning ultrasound measure in single-trait prediction models. When both weaning and yearling ultrasound measures were used to predict carcass fat thickness, partial [R.sup.2] values were 0.15 and 0.61 for weaning and yearling ultrasound fat thickness, respectively. The difference between predicted and carcass measures with respect to muscle area (fat thickness) was less than 6.45 [cm.sup.2] (2.5 mm) for 80.2 to 88.9% (90.3 to 95%) of animals. Preharvest ultrasound measures yielded standard errors of prediction of less than 4.95 [cm.sup.2] for muscle area and 1.51 mm or less for fat thickness. These results indicate that ultrasound measures taken between weaning and yearling provide accurate predictors of corresponding carcass traits in steers, bulls, and heifers. Key Words: Accuracy, Beef Cattle, Carcass Composition, Ultrasound

This study evaluated the effectiveness of a LHRH fusion protein vaccine on endocrine changes, feedlot performance, and carcass quality of bulls compared with steers and hormone-implanted steers. Crossbred bulls (n = 30; mean weight, 179 [+ or -] 4 kg; mean age, 130 [+ or -] 2 d) were randomly assigned to three treatment groups: 1) castrated (castrated; n = 10); 2) castrated-implanted with trenbolone acetate (implanted; n = 10); and 3) immunized against a cocktail of recombinant fusion proteins, ovalbumin-LHRH-7 and thioredoxin-LHRH-7 (immunized bulls; n = 10). Blood was collected every 2 wk to evaluate antibody and hormone concentrations. Serum LHRH antibodies (P < 0.001) were detected in animals of the immunized group, which had reduced serum LH concentrations (P < 0.001) compared with the castrated groups and serum FSH concentrations, which did not decrease but were significantly different when compared with castrated and implanted animals. Serum testosterone concentrations in the immunized bulls were not different from the two castrated groups (P > 0.05) by d 60 after primary immunization. Initial mean scrotal circumference of the immunized bulls was 18.0 [+ or -] 0.6 cm on d 0 and increased to 22.6 [+ or -] 1.3 cm by d 310. No differences (P > 0.05) in ADG were observed among treatment groups. Immunized animals had an intermediate BW gain (P > 0.05) when compared with the castrates, whereas the castrated groups differed (P < 0.05) from each other. Carcass characteristics were similar (P < 0.05) among the three groups. Vaccinating bulls against a LHRH fusion protein cocktail suppressed LH and testosterone, which led to reduced testicular development and no bullock carcasses. Growth and carcass characteristics of the immunized animals were similar to the steers. Key Words: Bulls, Carcass, Growth, Immunization, LHRH

To develop techniques for spermatogonial transplantation in bulls, it is essential to have an effective bioassay procedure to evaluate the transplantation efficiency of spermatogonial stem cell collection, purification, and culture techniques. The objective of the present study was to develop a mouse bioassay model to evaluate transplantation efficiency of fresh and cultured bovine germ cells. Bull calves of four ages (1, 2, 3, and 4 mo) were used as a source of donor testes cells. Two calves were used for each age point, one calf was experimentally made cryptorchidistic at 1 wk of age and the other left normal. A STO (mouse fibroblast) feeder cell line was used to culture bovine testes cells for 2 wk preceding transfer into recipient testes. Immunodeficient nude mice (nu/nu) in which endogenous spermatogenesis had been abolished by busulfan treatment served as recipient animals for transplantation. Donor bovine germ cells were microinjected into mouse seminiferous tubules. Mouse testes were analyzed 2 wk after transplant with the use of a bovine-specific antibody and whole-mount immunohistochemistry for the presence of bovine donor germ cells. Bovine testis cells were present in all recipient mouse testes analyzed. Fresh bovine testes cells were observed as colonies of round cells within mouse seminiferous tubules, indicating spermatogonial expansion and colonization; however, cultured bovine testes cells appeared as fibrous tissue and not as spermatogenic colonies. The average number of colonies resulting from donor cryptorchid testes was not different (P > 0.05) from noncryptorchid, 56 [+ or -] 4 and 78 [+ or -] 7, respectively. Fresh donor cells from calves older than 1 mo gave rise to a greater average number of colonies within recipient testes (P < 0.05) (1 mo, 33 [+ or -] 4; 2 mo, 70 [+ or -] 8; 3 mo, 63 [+ or -] 6; 4 mo, 87 [+ or -] 9). Fresh bovine germ cells are capable of colonization in the busulfan-treated nude mouse testis, making it a suitable model for evaluation and development of spermatogonial transplant techniques in bulls. Key Words: Bovidae, Spermatogonia, Transplantation

Recent studies on the structural composition of mammalian sperm heads have shown a congregate of unidentified proteins occupying the periphery of the mammalian sperm nucleus, forming a layer of condensed cytosol. These proteins are the perinuclear theca (PT) and can be categorized into SDS-soluble and SDS-insoluble components. The present study focused on identifying the major SDS-insoluble PT protein, which we localized to the subacrosomal layer of bovine spermatozoa and cloned by immunoscreening a bull testicular cDNA library. The isolated clones encode a protein of 122 amino acids that bears 67% similarity with histone H2B and contains a predicted histone fold motif. The novel amino terminus of the protein contains a potential bipartite nuclear targeting sequence. Hence, we identified this prominent subacrosomal component as a novel H2B variant, SubH2Bv. Northern blot analyses of SubH2Bv mRNA expression showed that it is testis-specific and is also present in murid testes. Immunocytochemical analysis showed SubH2Bv intimately associates, temporally and spatially, with acrosome formation. While the molecular features of SubH2Bv are common to nuclear proteins, it is never seen developmentally within the nucleus of the spermatid. Considering its developmental and molecular characteristics, we have postulated roles of SubH2Bv in acrosome assembly and acrosome-nuclear docking. Key Words: spermatozoa; perinuclear theca; spermiogenesis; acrosome development; histone; H2B; bipartite nuclear targeting sequence.

Over 2 yr, 45 Angus-sired steer offspring of Angus and Angus crossbred females were used to determine the effects of early weaning on feedlot performance, carcass characteristics, and economic return to the cow-calf enterprise. Steers were assigned by birth date to one of two weaning treatments: 1) weaned at an average age of 100 d (early weaned) or 2) weaned at an average age of 200 d (normally weaned). Within 36 d of weaning, steers were given ad libitum access to a high-concentrate diet (90% dry, whole-shelled corn). Steers were harvested when 12th-rib fat thickness averaged 1.27 cm within treatment as estimated by ultrasound. Carcass measurements were taken 48 h postmortem and rib steak tenderness was determined at 14 d postmortem by Warner-Bratzler shear force. Early-weaned steers had greater ADG from time of early weaning to normal weaning than suckling normally weaned steers (1.27 vs 0.86 kg/d, respectively; P < 0.001). However, early-weaned steers tended to have lower ADG for the entire finishing period than did normally weaned steers (1.33 vs 1.39 kg/d, respectively; P = 0.08). Compared with normally weaned steers, early-weaned steers had lower daily DMI (7.40 vs 5.95 kg/d, respectively; P < 0.001) and lower total DMI for the finishing period (1,618 vs 1,537 kg, respectively; P < 0.05). Early-weaned steers had greater gain:feed for the finishing period than normally weaned steers (0.223 vs 0.189, respectively; P < 0.001). Carcass weights were lighter for early-weaned steers than for normally weaned steers (277.9 vs 311.2 kg, respectively; P < 0.001). There was no difference in yield grade (3.1 vs 3.2; P < 0.10) between treatments. All carcasses graded Low-Choice or greater, and there was no difference in the percentage of carcasses grading Mid-Choice or greater (94.5 vs 83.9% for early- and normally-weaned, respectively; P > 0.10). Warner-Bratzler shear force values were similar between treatments. Early-weaned steers had a lower cost of gain than normally weaned steers ($ 0.82 vs 0.91/kg, respectively; P < 0.001). However, due to lighter carcass weights, early-weaned steers generated less return to the cow-calf enterprise than normally weaned steers ($ 380.89 vs 480.08/steer; P < 0.001). The early weaning of steers at 100 d of age decreased total DMI, improved gain:feed, and lowered the cost of gain; however, return to the cow-calf enterprise was decreased due to lighter carcass weights. Key Words: Age at Weaning, Beef Cattle, Fattening Performance, Carcass Quality, Economics, Tenderness

Our objective for this study was to assess the effect of recombinant bovine somatotropin (rbST) in overcoming the biological effects attributed to live weight increase and age on growth and fat deposition in male cattle. Holstein-Friesian bull calves (n = 56; 182.2 +/- 14.7 d old) were allotted to four subtreatments in a randomized complete block with a factorial arrangement of two levels of rbST: 0 and 500 mg of Posilac, every 2 wk, and two dietary metabolizable energy (ME) concentrations: low metabolizable energy (LME) and high metabolizable energy (HME); 10 vs 11.3 MJ/kg DM, respectively. The effect of rbST treatment on daily gain was expressed mostly on the HME diets. The rbST treatment had no effect on the animals fed the LME diets before the age of 240 d was reached. Dry matter intake and the effect of rbST treatment on DM intake were inversely related to the energy concentration of the diet. The degree of fatness of the animals was significantly reduced by rbST treatment and significantly increased by energy concentration of the diet. The major effect of rbST, under the experimental conditions, in regards to adipose tissue deposition, was on the fat depots and not on the intramuscular fat. The concentration of bST, IGF-I, and insulin in the plasma was increased (P < .001) owing to rbST treatment. Lower metabolizable energy supply led to a higher (P < .001) plasma bST concentration, nonsignificantly lower plasma IGF-I and thyroid hormone concentrations, and lower (P < .001) plasma insulin concentration. A trend (P = .065) toward an increase in PUFA was found in the muscle of the rbST-treated and the HME diet animals. At a young age, when the natural growth potential is high, rbST treatment will be efficient only when a diet allowing a high digestible energy intake is provided. Key Words: Dairy Bulls, Somatotropin, Beef, Age, Energy

Byline: S. Fritsche (1), G. Schmidt (1), H. Steinhart (1) Keywords: Key wordsaHormone pattern; Gas chromatography-mass spectrometry; Beef; Bulls; Steers Abstract: aA rapid and economical method was developed for the simultaneous determination of androgens, progestogens, and glucocorticoids and their precursors and metabolites in meat. Steroids were isolated with liquid extraction followed by C.sub.18-solid-phase extraction (C.sub.18-SPE). Corticoids were separated from the less polar steroids by Si-SPE. The non-polar steroids required additional purification by filtration through an NH.sub.2 cartridge. The fractions were combined and derivatized with a universally applicable trimethylsilylation of both hydroxyl and keto groups. Determination was performed with gas chromatography-mass selective detection (determination limits: 0.02--0.1ug/kg). Hormone profiles of 15 muscle tissue samples of both bulls and steers were analysed. Beef from bulls contained higher concentrations of testosterone and epitestosterone (P&lt 0.001), 11-deoxycorticosterone (P&lt 0.01), androstenedione (P&lt 0.05) and cortisone (P&lt 0.05), and significantly lower proportions of cortisol (P&lt 0.001) than beef from steers. Author Affiliation: (1) University of Hamburg, Institute of Biochemistry and Food Chemistry, Grindelallee 117, D-20146 Hamburg, Germany e-mail: fc6a070@lc.chemie.uni-hamburg.de, DE Article note: Received: 21 April 1998

This investigation gives an overview of the concentrations of naturally occurring androgens, progestogens, corticesteroids, and their precursors and metabolites in meat from bulls and steers. A recently developed gas chromatography-mass spectrometry (GC-MS) method with improved sensitivity for steroid analysis was used. Eighty-two beef samples were analyzed using the GC-MS method. Beef from bulls contained higher concentrations of testosterone, which is an anabolic androgen, and its metabolite epitestosterone (P < .01) and the androgen precursor dehydroepiandrosterone (P < .05) than beef from steers. Beef from steers contained higher (P < .05) concentrations of the basic hormone precursor pregnenolone and cortisol, which is a catabolic corticosteroid, than beef from bulls. A classification of an unknown beef sample to one of the categories (bull or steer) was possible in most cases (>90%) using a masculinity index (MI) that was calculated using the concentrations of testosterone, epitestosterone, and pregnenolone. Because the hormonal status of beef cattle is related to meat quality characteristics, such as tenderness or fat and protein distribution, the MI may contribute to meat quality assessment and meat quality control. Key Words: Beef, Steers, Bulls, Androgens, Progestogens, Corticoids

Mixed linear models were developed by animal breeders to evaluate genetic potential of bulls. Application of mixed models has recently spread to all areas of research, spurred by availability of advanced computer software. Previously, mixed model analyses were implemented by adapting fixed-effect methods to models with random effects. This imposed limitations on applicability because the covariance structure was not modeled. This is the case with PROC GLM in the SAS[R] System. Recent versions of the SAS System include PROC MIXED. This procedure implements random effects in the statistical model and permits modeling the covariance structure of the data. Thereby, PROC MIXED can compute efficient estimates of fixed effects and valid standard errors of the estimates. Modeling the covariance structure is especially important for analysis of repeated measures data because measurements taken close in time are potentially more highly correlated than those taken far apart in time. Key Words: Statistical Analysis, Direct Sire Comparisons, Analysis of Variance

Metabolism of muscle growth in the hindquarter was investigated by the arterio-venous difference (AVD) technique in Belgian Blue double-muscled type bulls at maintenance or at fattening. The bulls were fitted with an aortic ultrasonic blood flow probe and with catheters in the aorta and vena cava. They were offered a diet allowing for maintenance (MP) during a period of 15 d, at the end of which measurements were made over 3 d. Bulls were then given a fattening diet (FP) and the measurements were repeated. Arterial blood flow was approximately 1 L/min greater when the bulls were standing than when lying. Blood flow was 2 L/min higher during FP than during MP. The AVD and uptake of glucose were maximal at 1400 and 1600. Uptake of [Alpha]-amino nitrogen decreased immediately after a meal. The increase in glucose from MP to FP fitted very well with the calculated energy needs for muscle growth. The AVD and uptake of [Alpha]-amino nitrogen, total amino acids, and total nonessential amino acids were negative during MP and positive and significantly higher during FP. There was also a significant increase in AVD and uptake of essential and branched-chain amino acids when the bulls were changed from MP to FP. When changing from maintenance to fattening, the incremental glucose and amino acid hindquarter uptake provided energy and supply for muscle protein accretion, respectively. The level of alanine transamination was also sharply reduced. Key Words: Belgian Blue, Catheterism, Growth Rate, Metabolites

To determine the effect of prepubertal immunization against GnRH on the development of sexual and social behavior of Friesian bulls, 90 calves were randomly assigned to five treatments: 1) [I.sub.2], immunized against GnRH at 2 and boosted at 2.5, 4, and 7.5 mo of age, n = 2 x 10; 2) [I.sub.4], immunized against GnRH at 4 and boosted at 4.5 and 7.5 mo of age, n = 2 x 10; 3) [I.sub.7.5], immunized against GnRH at 7.5 and boosted at 8 mo of age n = 2 x 10; 4) S, steers castrated at 2 mo of age, n = 10; and 5) B, intact bulls, n = 2 x 10. Blood samples were collected initially every 2, then every 3 wk. Plasma was analyzed for anti-GnRH titers and plasma testosterone concentration. Sexual and agonistic behavior, male-male mounting, and damage to paddocks was assessed throughout the experiment. All immunized calves developed antibodies against GnRH (32.3 [+ or -] 2.0% bound at a 1:10 plasma:PBS-BSA dilution, 14 d after first boost). Plasma testosterone concentrations were < 1 ng/mL for all immunized animals until 11 mo of age, when they increased to levels found in intact bulls at 14 mo of age. At slaughter, testes and seminal vesicle weights were 38.3 and 31.6% lighter, respectively, for all immunized treatments compared to B. There were no significant differences between [I.sub.2], [I.sub.4], and [I.sub.7.5] in any of the sexual or agonistic behavior tests. Bulls scored higher than steers in all sexual behavior tests. Immunized bulls scored lower than bulls in sexual behavior tests from 10 to 17 mo of age. The proportion of immunized animals that serviced an estrous cow was lower than the proportion of intact bulls at 10, 12.5, 14, and 17 mo of age. Immunized animals scored lower than bulls in bull challenge tests at 8.5, 11.5, 13, 14.5, and 17 mo of age. Paddock damage by animals on the three immunization treatments was lower than that by bulls from 7 to 14.5 mo of age, as were leg wear scores (an indicator of male-male mounting behavior) from 9 to 14 mo of age. There was no difference in sexual behavior between immunized bulls ([I.sub.2], [I.sub.4], and [I.sub.7.5]) and bulls while held in lairage pens for 16 h before slaughter, but all treatment groups scored higher than steers. There was a similar trend for agonistic behavior, although [I.sub.4] bulls were no different from steers. Prepubertal immunization against GnRH at 2, 4, and 7.5 mo of age impaired testes function and affected the development of social and sexual behavior of young bulls. Key Words: Immunization, GnRH, Bulls, Steers, Behavior, Testosterone

Comparisons involving Brahman and Brahman-derivative (Brangus, Santa Gertrudis, Beefmaster, Simbrah, Braford) sires indicate the following: 1) cows mated to Brangus and Santa Gertrudis bulls had a shorter gestation length than cows mated to Brahman bulls, 2) calves sired by Brangus and Beefmaster bulls were lighter at birth and weaning than calves sired by Brahman bulls, and 3) birth and weaning weights were similar for calves sired by Santa Gertrudis and Brahman bulls and for calves sired by Simbrah and Brahman bulls. Comparisons involving Brahman and other Zebu (Sahiwal, Nellore, Gir, Indu-Brazil, Boran, Romana Red) sires indicate that gestation length was slightly longer for cows mated to Sahiwal and Nellore bulls and that, relative to the Brahman, birth and weaning weights were similar to or lighter for calves sired by bulls of the other Zebu breeds. The only exception to this pattern was birth weight of Indu-Brazil-sired calves, which were heavier than calves sired by Brahman bulls. Comparisons involving Brahman and non-Zebu subtropically adapted (Tuli, Senepol) sires indicate that cows mated to Tuli bulls had a slightly shorter gestation length than cows mated to Brahman bulls and that birth and weaning weights of calves sired by Tuli and Senepol bulls were lighter than those of calves sired by Brahman bulls. Key Words: Cattle, Brahman, Subtropics, Adaptation

The objective was to determine the effects of reducing the plasma cortisol rise in calves following castration on plasma ACTH concentrations, keyhole limpet hemocyanin (KLH)- and concanavalin A (Con A)-induced in vitro interferon (IFN)-[Gamma] production, white blood cell (WBC) numbers, neutrophil:lymphocyte (N:L) ratio, plasma haptoglobin and fibrinogen concentrations, ADG, and ADFI. Forty 5-mo-old Friesian bull calves (169 [+ or -] 1.7 kg) were assigned to four treatments: 1) control (CON); 2) oral metyrapone administration (MET); 3) surgical castration at 0 h on d 0 (SURG); and 4) oral metyrapone administration and surgical castration (MET + SURG). Cortisol, ACTH, IFN-[Gamma] production, haptoglobin, fibrinogen, ADFI, and ADG were not different between CON and MET animals. The MET + SURG calves had lower (P < .001) peak and mean cortisol during .25 to 1.5 h than SURG animals, but area under the cortisol vs time curve from 0 to 12 h did not differ (P > .39) between SURG and MET + SURG calves. Peak ACTH concentrations and area under the ACTH vs time curve from 0 to 6 h were greater (P < .05) for MET + SURG than for SURG calves. There were no differences between MET + SURG and SURG animals in IFN-[Gamma] production, WBC numbers, and ADFI. On d 1, MET + SURG and SURG animals had lower (P Key Words: Cattle, Stress, Hydrocortisone, Castration, Metyrapone, Interferon

The objective of this study was to determine the effect of dietary energy, breed (British vs Continental x British crosses), and their interactions on scrotal surface temperature (SST), seminal quality, and sperm production in bulls. This experiment, replicated over 2 yr, included 72 Angus, Angus x Simmental, or Hereford x Simmental bulls fed either a moderate- (100% forage) or high-energy (80% grain, 20% forage) diet for 168 d after weaning. At the end of the feeding period, SST was determined by infrared thermography, seminal samples (two ejaculates) were collected by electroejaculation, and reproductive tracts were collected at slaughter. Bulls fed the high-energy diet were heavier (P < .0001; diet x time interaction), had thicker backfat (P < .05; diet x line x time interaction), and had a larger scrotal circumference(P < .05). Testicular tone decreased over time (P < .0001) with a diet x time interaction (P < .05). There was no significant effect of diet on top, bottom, or average SST. However, bulls fed the moderate-energy diet had a larger (P < .02) SST gradient (3.9 vs. 3.4 [degrees] C). Bulls fed the moderate-energy diet had more (P < .01) morphologically normal spermatozoa (68.8 [+ or -] 2.1 vs 62.5 [+ or -] 2.5%) and a higher proportion (P < .006) of progressively motile spermatozoa (53.4 [+ or -] 2.1 vs 44.5 [+ or -] 2.4%). No effects (P > .05) of dietary energy on epididymal sperm reserves or daily sperm production were detected. Increased dietary energy may affect scrotal or testicular thermoregulation by reducing the amount of heat that can be radiated from the scrotal neck, thereby increasing the temperature of the testes and scrotum. Key Words: Testes, Scrotum, Thermoregulation, Diet, Energy, Bulls

A monoclonal antibody (M1) was produced against seminal fluid heparin-binding proteins (HBP) from a vasectomized bull. In the first part of this study, the presence of HBP in sperm or seminal fluid was determined for 53 bulls with an ELISA using M1. Bulls (8 to 18 per pasture) were bred to 1,114 cows at ratios of 1 bull:25 cows. Bulls with detectable HBP on sperm membranes were 11 percentage points more fertile than bulls with undetectable HBP in sperm membranes. In the second part of this study, three sperm membrane HBP approximately 30, 24, and 21.5 kDa were identified with Western blots using M1. Santa Gertrudis bulls (n = 64) were bred to 1,354 Santa Gertrudis cows in groups with 2 to 11 bulls. Bulls with those three HBP (Group A) or a single 30-kDa HBP (Group B) in sperm membranes had the greatest fertility, ranging from 74.4 to 89.9% (mean = 81.5%) of the palpated cows that were pregnant. Bulls with the 21.5- and 30-kDa HBP (i.e., the 24-kDa HBP was absent; Group C) had a reduced fertility of 61.3%. Bulls without detectable HBP (Group D) resulted in 41.9% of 186 cows palpated pregnant. Bulls in Groups A and B were more (P < .01) fertile than all other groups. In conclusion, the presence of HBP in sperm membranes was indicative of the fertility potential of bulls. Key Words: Bulls, Fertility, Heparin-Binding Proteins, Spermatozoa, Monoclonal Antibodies

Energy and protein retained in 50, 38, and 54 nonimplanted Holstein and Angus heifers, steers, and bulls, respectively, 17 pens (237 cattle) of beef breed implanted heifers, and 65 pens (535 cattle) of beef breed implanted steers were compared to values predicted by the 1984 National Research Council (NRC), Cornell Net Carbohydrate and Protein System (CNCPS), and the model of Oltjen et al. (OLTJEN). The NRC accounted for 83, 85, 86, 88, and 88% of the variation in retained energy (RE) with biases of -8, +13, -6, +6, and -12% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. The CNCPS accounted for 93, 98, 92, 95, and 91% of the variation in RE with biases of +2, +10, -6, +1, and -13% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. OLTJEN accounted for 78, 76, 48, 93, and 96% of the variation with biases of -3, -2, +9, -8, and -1% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. For retained protein (RP), the NRC accounted for 57, 68, 70, 86, and 84% of the variation with biases of -12, -7, +16, -8, and -10% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. The CNCPS accounted for 69, 77, 84, 94, and 84% of the variation in RP with biases of -7, -11, 0, -3, and -9% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. OLTJEN accounted for 51, 38, 0, 35, and 69% of the variation with biases of -23, -2, -31, -4, and -38% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. This analysis indicates that the CNCPS, which uses a weight adjusted for body size and sex in the NRC 1984 medium-frame steer equation, can be used to predict both RE and RP for all classes of cattle (implanted and nonimplanted heifers, steers, and bulls varying in body size) when their weights are adjusted to that equivalent to the body size steer represented by that equation.

This study was conducted to test the hypothesis that administering recombinant bovine somatotropin (rbST) would affect testicular development in Holstein bulls. From 4 until 32 wk of age, bulls received a daily injection of either placebo (C) or rbST (.2 mg/kg [BW.sup..75], i.m.; n = 10/group). At 14-d intervals, blood was obtained and assayed for testosterone (T); BW, shoulder height (SH), and testis length (TL) were recorded. At 7, 12, and 24 wk of age, bulls were bled at 10-min intervals for 6 h to determine the secretory patterns of LH, growth hormone (GH), and IGF-I. All bulls were killed at 40 wk of age. One testis was used for determination of daily sperm production (DSP), and the number of spermatids per gram of parenchyma (SP/G); the remaining testis was perfused and fixed for histological analysis of numbers of Sertoli cell nuclei (SCN/ST) and spermatids per seminiferous tubule crosssection (SP/ST). Epididymal spermatozoa were collected to test effects of rbst on the integrity of spermatozoal chromatin structure. Administration of rbST increased (P < .0001) concentrations of GH (nanograms/milliliter) in plasma at all ages (C vs rbST; wk 7, 8.9 [+ or -] 1.0 vs 51.9 [+ or -] 6.8; wk 12, 12.8 [+ or -] 1.4 vs 59.2 [+ or -] 6.4; and wk 24, 5.2 [+ or -] 1.5 vs 42.6 [+ or -] 12.2). There was an age x treatment interaction (P < .0183) for concentrations of IGF-I (nanograms/milliliter) in plasma (C vs rbST; wk 7, 149.7 [+ or -] 6.1 vs 148.6 [+ or -] 8.6; wk 12, 184.1 [+ or -] 12.8 vs 216.6 [+ or -] 15.9; and wk 24, 392.8 [+ or -] 24.8 vs 484.7 [+ or -] 19.9). No differences due to rbST treatment were observed for T, BW, SH, or TL or for the secretory pattern of LH at 7, 12, or 24 wk. Treatment with rbst did not affect DSP, SP/G, SCN/ST, or SP/ST or integrity of spermatozoal chromatin. We conclude that administering .2 mg/kg [BW.sup..75] of rbST throughout the period of Sertoli cell differentiation and replication results in no detectable differences in selected variables of sexual development. Key Words: Bulls, Testicular Development, Somatotropin, IGF-I

The effect of implants containing anabolic steroid (Synovex|R~) on testis function, feedlot performance, and carcass traits was evaluated in bulls, steers, and bulls actively immunized against gonadotropin-releasing hormone (GnRH). Ninety-one Hereford or Hereford x Red Angus bull calves were randomly assigned to a 3 x 2 factorial experiment. The treatments were 1) unimmunized control (n = 30), 2) actively immunized against GnRH (n = 31), or 3) castrate (n = 30). The classes were 1) unimplanted (n = 45) or 2) implanted (n = 46) with Synovex. Animals in treatment Groups 2 and 3 were either immunized with a GnRH-keyhole limpet hemocyanin (KLH) conjugate or castrated at 3.6 |+ or -~ .1 mo of age. Animals assigned to Class 2 received Synovex-C at the time of initial treatment and Synovex-S at weaning and feedlot entry. Animals in treatment Group 2 received a booster immunization at feedlot entry. Anti-GnRH titer was evident at weaning and remained elevated to slaughter in all (31 of 31) immunized animals. Anti-GnRH titer was not evident in steers or unimmunized bulls. Immunization and(or) Synovex decreased (P |is less than~ .05) serum concentrations of testosterone (T) and scrotal circumference (SC) at weaning. Similarly, SC, testis weight, and tissue concentrations of spermatozoa at slaughter were significantly reduced by immunization, Synovex, or the immunization/Synovex combination. Immunization, but not Synovex, reduced (P |is less than~ .05) serum levels of T at slaughter. The masculinity of immunized bulls was less (P |is less than~ .05) than that of control bulls. The final live weight and carcass weight of immunized bulls, regardless of implant class, and implanted steers did not differ (P |is greater than~ .05) from the slaughter and carcass weights of unimplanted control bulls. However, the final live weight, carcass weight, and feedlot gain of unimplanted steers was lower (P |is less than~ .05) than the slaughter and carcass weights and feedlot gain of control or immunized bulls or steers with Synovex implants. Immunization, like Synovex, reduced (P |is less than~ .05) the masculinity of the carcasses of bulls. Taken together, these data indicate that immunization against GnRH may have practical utility as a noninvasive alternative to surgical castration in management of beef cattle. In addition, the residual levels of T secretion in immunized bulls may have anabolic effects that reduce the need for supplementation with exogenous steroid.

The objectives of this study were to determine 1) the effect of bull:heifer ratio on reproductive performance and associated costs and returns on heifers in synchronized estrus and 2) the effect of estrus synchronization on reproductive performance and economic variables, in a multiple-sire, pasture breeding situation. Eight hundred yearling beef heifers and 28 mature, sexually experienced beef bulls were allotted to four treatments (two replicates per treatment) at bull:heifer ratios of 2 per 100 (1:50; Treatment 1), 2 per 100 (1:50; Treatment 2), 4 per 100 (1:25; Treatment 3), and 6 per 100 (1:16; Treatment 4). Treatment 1 (control) used nonsynchronized heifers, whereas heifers in Treatments 2, 3, and 4 were synchronized using the 33-d melengestrol acetate (MGA)-prostaglandin F(sub 2 alpha (PGF(sub 2 alpha) program. Pregnancy results after a 28-d breeding season indicate that there may be a limit to how many estrus-synchronized heifers bulls can impregnate. Treatment 2 showed a 6% decrease (P < .10) in pregnancy rate (77%) compared with Treatment 3 (83%), indicating that the bulls probably were not able to service all the synchronized heifers. Treatments 3 and 4 had similar pregnancy rates (83 and 84%, respectively). Treatment 4 had a 3-d advantage (P < .01) over Treatment 3 in average day of conception. However, based on economic analysis, Treatment 3 exhibited greater returns. Estrus synchronization failed to provide any advantage in pregnancy rate or day of conception. For unknown reasons, the control, nonsynchronized heifers cycled and conceived as if they were synchronized. Treatment 2 had a 5% decrease in pregnancy rate compared with Treatment 1 (77 vs 82%; P < .10) with no difference in average day of conception. Consequently, Treatment 1 (nonsynchronized) exhibited greater economic returns. Results of this study indicated that the optimal bull:heifer ratio for estrus-synchronized heifers was 1:25. In this study, estrus synchronization failed to provide an advantage in terms of reproductive performance or economic efficiency.

Sixty Brangus bulls were evaluated live using two real-time ultrasound instruments and four technicians to estimate longissimus muscle area (LMA) and 12th rib fat thickness (FT) every 4 mo beginning at 4 and 12 mo of age, respectively, and continuing until 24 mo of age. Ten bulls were slaughtered every 4 mo to determine actual LMA and FT, 9-10-11th rib chemical composition, yield grade (YG) factors, and empty body weight (EBW). Live animal traits were used to predict 9-10-11th rib composition, YG, and EBW. Scanned mean FT was accurate (P < .05) at 16 mo and was not different (P = .09) from the actual mean FT (95% of the time the error in estimation was less than or equal to 33 cm). Scanned mean LMA was accurate (P < .05) at 12 mo (95% of the time the error in estimation was less than or equal to 20.0 cm squared). Absolute differences between scanned and actual mean FT and LMA were different (P < .05) from zero for the main effects of month, operator and(or) interpreter, and instrument. Increased level of operator skill did not improve the accuracy of FT or LMA measurements, whereas increased level of skill of the interpreter of scans did improve the accuracy of LMA estimations. There was no difference (P > .05) between ultrasound instruments in accuracy of estimating FT or LMA. The most accurate prediction of YG occurred at 12 mo and incorporated LW, hip height (HH), and ultrasound LMA (R squared = .95, SD = .14). The most accurate prediction of EBW occurred at 16 mo and incorporated LW, HH, and ultrasound FT (R squared = .99, SD = 6.65 kg), whereas the most accurate equation for combined slaughter periods incorporated LW, HH, and ultrasound LMA (R squared = .99, SD = 20.71 kg). We conclude that scanning of LMA at 12 mo and of FT at 12 or 16 mo were sufficiently accurate to characterize groups of bulls; however, some individual measurements were quite inaccurate. Measurements at other months should not be considered accurate for either individuals or groups of bulls. Yield grade and EBW can be accurately estimated from live animal and ultrasound measurements, which may be useful in identifying Brangus cattle with superior cutability and may eliminate the need for serial slaughter in research projects.

Gonadotropin-releasing hormone-keyhole limpet hemocyanin conjugate (GnRH-KLH) immunization has better effects on bulls and steers as compared to surgical castration especially prior to testicular development. Antibodies against GnRH were detected within six weeks and peak levels were detected at 16 to 20 weeks post-immunization. Feeding and carcass quality are not affected by the GnRH-KLH. Active immunization against GnRH resulted in reduced testicular growth while perfomance traits and serum LH levels were unaffected. Castration resulted in decreased perfomance and carcass quality which was partially reversed by anabolic steroids.

Implants containing the hormone 17-beta-estradiol (E2) were administered to gonadectomized cows and bulls to determine the influence of E2 on the serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations and patterns. Low E2 doses enhanced LH and FSH concentrations. However, higher concentrations significantly reduced the circulating concentrations of the LH and FSH. Estradiol effect on FSH levels was found to be greater in bulls than in cows.