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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

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

The objectives of this study were to characterize feed efficiency traits and to examine phenotypic correlations between performance and feeding behavior traits, and ultrasound measurements of carcass composition in growing bulls. Individual DMI and feeding behavior traits were measured in Angus bulls (n = 341; initial BW = 371.1 [+ or -] 50.8 kg) fed a corn silage-based diet (ME = 2.77 Mcal/kg of DM) for 84 d in trials 1 and 2 and for 70 d in trials 3 and 4 by using a GrowSafe feeding system. Meal duration (rain/d) and meal frequency (events/d) were calculated for each bull from feeding behavior recorded by the GrowSafe system. Ultrasound measures of carcass 12th-rib fat thickness (BF) and LM area (LMA) were obtained at the start and end of each trial. Residual feed intake (RFIp) was computed from the linear regression of DMI on ADG and midtest [BW.sup.0.75] (metabolic BW, MBW), with trial, trial by ADG, and trial by midtest [BW.sup.0.75] as random effects (base model). Overall ADG, DMI, and RFIp were 1.44 (SD = 0.29), 9.46 (SD = 1.31), and 0.00 (SD = 0.78) kg/d, respectively. Stepwise regression analysis revealed that inclusion of BW gain in BF and LMA in the base model increased [R.sup.2] (0.76 vs. 0.78) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted residual feed intake (RFIc) were moderately correlated with DMI (0.60 and 0.55, respectively) and feed conversion ratio (FCR; 0.49 and 0.45, respectively), and strongly correlated with partial efficiency of growth (PEG; -0.84 and -0.78, respectively), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (-0.15), and PEG (-0.11), but not with RFIc. Gain in LMA was weakly correlated with RFIp (0.17) and FCR (-0.19), but not with PEG or RFIc. The Spearman rank correlation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp and accounted for 35% of the variation in DMI not explained by MBW, ADG, and ultrasound traits (RFIc). These results suggest that adjusting residual feed intake for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composition of gain. Key words: Angus bull, carcass composition, feeding behavior, residual feed intake

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

The objective was to compare testis characteristics of Zebu bulls treated with the GnRH agonist, deslorelin, at different times and for different durations during their development. An additional objective was to determine the usefulness of a stain for the transcription factor GATA-binding protein 4 (GATA-4) as a specific marker for Sertoli cell nuclei in cattle. Bulls (54) were allocated to nine groups (n = 6) and received s.c. deslorelin implants as follows: G1 = from birth to 3 mo of age; G2 = from 3 to 6 mo; G3 = from 6 to 9 mo; G4 = from 9 to 12 mo; G5 = from birth to 15 mo; G6 = from 3 to 15 mo; G7 = from 6 to 15 mo; G8 = from 12 to 15 mo; and G9 (control) = no implant. Bulls were castrated at 19 mo of age. Paraffin sections (10 [micro]m) were subjected to quantitative morphometry and GATA-4 immunohistochemistry. At castration, all bulls in the control group (6/6) had attained puberty (scrotal circumference [greater than or equal to] 28 cm), whereas a smaller proportion (P < 0.05) had reached puberty in G2 (2/5) and G6 (1/ 6). Bulls in G2 and G6 also had a lesser (P < 0.05) testis weight compared with the control group. Total volume of seminiferous epithelium and total daily sperm production in G2 and G6 were only half that observed in the control group. Spermatids were observed in less than 50% of seminiferous tubules in G2, G6, and G7 compared with 82% in the control group (P < 0.05). Staining for GATA-4 was specific for and abundant in the Sertoli cell nucleus in both pre- and postpubertal bulls, and no other cell nucleus inside the seminiferous tubule was positive for GATA-4. Total number of Sertoli cells was not affected by treatment (P = 0.45), but nuclear volume was smaller in G2 and G6 (P < 0.05) compared with the control group. In conclusion, treatment of Zebu bulls with deslorelin had no apparent beneficial effect on testis development and delayed puberty when treatment was initiated at 3 mo of age. Staining for GATA-4 was a useful method for identifying and quantifying Sertoli cell nuclei in both pre- and postpubertal bulls. Key Words: GATA-Binding Protein 4, Gonadotropin-Releasing Hormone, Male Sexual Function, Sertoli Cells, Testis Development, Zebu Cattle

The three-step technique was used to determine the requirements of total amino acids (TAA) and the first-limiting amino acid (AA) in growing double-muscled Belgian Blue bulls (BBb). In Exp. 1, three double-muscled BBb weighing initially 306 +/- 28 kg received a basal diet consisting of 30% meadow hay and 70% concentrate that was poor in digestible protein but had adequate NE because of continuous infusion of dextrose into the duodenum. The intestinal apparent digestibility of essential AA (EAA) was defined according to their duodenal and ileal flows. It averaged 72% but varied between 60% for Met and 79% for Arg. In Exp. 2, five double-muscled BBb (334 +/- 22 kg) received the same diet supplemented with duodenal infusions of dextrose and four doses of Na-caseinate (28, 56, 84, and 112% of intestinal digestible dietary AA) in a 4 x 4 Latin square design with one additional animal. Nitrogen retention for the basal diet alone and the four increasing supplements of Na-caseinate reached 49, 61, 70, 80, and 86 g/d, respectively. Nitrogen utilization improved from 34.3% without Na-caseinate supplementation to a maximum of 40.6%, with the third dose supplying 788 g/d of apparently digestible AA. Based on patterns of plasma concentrations, Met, Phe, and Arg were probably the limiting AA when animals optimized N utilization. In Exp. 3, six double-muscled BBb (315 +/- 25 kg) fed the basal diet received duodenal infusions of dextrose and AA, equivalent to the third dose in Exp. 2, except for digestible Met (9.3, 14.4, 18.4, 22.4, 26.4, and 30.4 g/d) in a 6 x 6 Latin square design. The Met requirement was close to 26.4 g/d on the basis of N retention. Key Words: Ruminants, Amino Acids, Duodenum, Requirements, Plasma, Nitrogen

The objectives of this study were to examine differences in scrotal circumference, sperm motility, and percentage of normal sperm cells between two lines of Angus beef cattle divergently selected for blood serum IGF-I concentration. Data were obtained from an ongoing experiment involving 100 spring-calving (50 high and 50 low line) and 100 fall-calving (50 high and 50 low line) purebred Angus cows. Scrotal circumference, percentage of motile sperm cells, and percentage of normal sperm cells did not differ between high and low IGF-I line yearling bulls (P = .79, .50, and .56, respectively). The IGF-I concentrations measured at d 28, 42, and 56 of the postweaning test are abbreviated as IGF28, IGF42, and IGF56, respectively. Coefficients for the quadratic regression of scrotal circumference on IGF28 and IGF42 tended to be negative (P = .07 and .08, respectively), as did the coefficient for the quadratic regression of the percentage of motile sperm cells on IGF42 (P = .08). The coefficient for the linear regression of percentage of normal sperm cells on IGF28 was positive (P = .02). The coefficient for the quadratic regression of percentage of normal sperm cells on IGF56 was negative (P = .04). Coefficients for the quadratic regression of scrotal circumference and percentage of normal sperm cells on mean IGF-I concentrations were negative and important (P = .04 and .08, respectively). Thus, scrotal circumference and percentage of normal sperm cells are related to blood serum IGF-I concentration in yearling Angus bulls. Key Words: Beef Cattle, Insulin-Like Growth Factor, Selection, Scrotum, Spermatozoa

In each of 2 yr, 20 Holstein steers (185 [+ or-] 7 kg initial BW) were allocated to each of three treatments: pastured for 4.5 mo on grass/legume pastures and then fed 80% corn diets (DM basis) until slaughter; pastured for 4.5 mo on grass/legume pastures with ad libitum access to molasses-based protein supplements and fed 80% corn diets until slaughter; and placed in a feedlot and fed only 80% corn diets until slaughter (FEEDLOT). Half of the steers in each treatment were initially implanted with Revalor-S and not reimplanted. Supplemented steers on pasture had greater (P [is less than] 0.05) ADG than unsupplemented steers, and FEEDLOT steers gained faster and were fatter (P [is less than] 0.05) after 4.5 mo. Implanted steers had greater (P [is less than] 0.05) ADG with no significant treatment x implant status effect. Supplement intake was variable and related to ambient temperature. During the feedlot phase, steers previously on pasture had greater DMI and ADG (P [is less than] 0.05) but were not more efficient than FEEDLOT steers. Percentage of USDA Choice carcasses, fat thickness, dressing percentage, yield grade, and final weight were greater (P [is less than] 0.05) for FEEDLOT steers than for steers on other treatments. Implanting increased ADG of all steers but did not affect carcass traits, carcass composition, or feedlot performance during the finishing phase. Holstein steers consuming supplemented and unsupplemented pasture before slaughter will be leaner, have lower carcass weights, and have generally lower quality grades than those fed exclusively in a feedlot when slaughtered at similar ages. Key Words: Carcass Quality, Grazing, Holstein, Liquid Diets

Seventy Angus x Simmental crossbred calves (initial BW 166.2 [+ or -] 4.2 kg) were used in a 3 x 2 factorial arrangement of treatments to determine the effect of age at feedlot entry and castration on growth, performance, and carcass characteristics. At 82 d of age (5-26-99), calves in the steer group were castrated. Calves were placed in the feedlot at 110 d of age (EW), 202 d of age (NW), or 371 d of age (Y). Calves in the NW and Y group remained with their dams until 188 d of age, and consumed pasture until feedlot entry (202 and 371 d of age; respectively). Steers were implanted with Synovex-S[R] (when steers were approximately 93 d from their terminal implant), and with Revalor-S[R] (when steers were estimated to be 100 d from slaughter). Calves were slaughtered on an individual basis when backfat was estimated to be 1.3 cm. While in the feedlot, Y calves gained faster (P0.22) was similar for age groups; however, daily DMI was the lowest for EW, intermediate for NW, and the highest for Y calves (7.1, 8.1, 10.5 kg/d; P Key Words: Feedlot Age, Bulls, Steers