Influence of zeranol implants on growth, behavior and carcass traits in Angus and Limousin bulls and steers

A 2(3) factorial arrangement of treatments was utilized to determine effects of postweaning zeranol implantation, breed (Angus vs Limousin) and castration (bull vs steer) on growth, behavior and carcass traits. An initial slaughter group was used to account for breed differences in composition and to determine fat and lean growth in the 9-10-11th rib section (NTE). The remaining cattle were fed a finishing diet to a fat end point of .76 cm, as determined by a backfat probe. Control bulls outgained (P less than .01) control steers both to the first kill date and over the entire test and did not require significantly more time to reach the fat end point. The implant did not influence gain in bulls but did increase gain in steers. Angus and Limousins were similar in growth rate for the first 126 d before the first slaughter date. Limousins required more (P less than .01) time to reach the fat end point. Bulls and Limousins produced heavier (P less than .01) carcasses and larger rib eyes (P less than .05; bulls; P less than .01; Limousins). Steers and Angus had higher (P less than .01) marbling scores and lower bone maturity. Implanting decreased (P less than .05) marbling and increased carcass maturity. Small but significant shifts in carcass wholesale cut weight distribution were found between breed and sex condition groups. Bulls and Limousins had greater lean growth in the NTE. Bulls and steers were similar in fat growth, but Angus exceeded Limousin in this trait. Zeranol reduced scrotal circumference (P less than .01) and testicle weight at slaughter (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of two beta-adrenergic agonists on finishing performance, carcass characteristics, and meat quality of feedlot steers

The impact of using 2 beta-adrenergic agonists in feedlot cattle fed finishing diets was evaluated using 54 steers (45 crossbred Charolais and 9 Brangus) initially weighing 424 +/- 26.6 kg in a randomized complete block design with 3 treatments and 6 blocks (i.e., 18 pens with 3 steers per pen). Response variables were feedlot performance, carcass characteristics, and meat quality. Treatments were 1) control (no supplement added); 2) zilpaterol hydrochloride (ZH; 60 mg.steer(-1).d(-1)); and 3) ractopamine hydrochloride (RH; 300 mg.steer(-1).d(-1)). The beta-agonists were added to the diets during the final 33 d of the experiment. The groups of steers fed ZH or RH improved (P < 0.01) ADG by 26 or 24%, respectively, compared with control steers. Steers supplemented with RH consumed less (P = 0.03) DM (8.37 kg) than control steers (8.51 kg), whereas intake was similar (P = 0.37) for ZH and control steers. Addition of either beta-agonist to the diet considerably improved (P < 0.01) the G:F (ZH, 0.253 and RH, 0.248 vs. control, 0.185). Hot carcass weight and carcass yield were enhanced (P < 0.05) with both beta-agonists. The LM area was increased (P = 0.026) by ZH (75.2 cm(2)), but that of RH (72.2 cm(2)) was similar (P = 0.132) to the control steers (66.8 cm(2)). Meat from the ZH- (P = 0.0007) and RH- (P = 0.0267) supplemented steers had greater shear force values than control steers (ZH = 5.11; RH = 4.83; control = 4.39 kg/cm(2)). Variables related to meat color indicated that both beta-agonists led to a similar redness of the LM area related to the control group. In general, feedlot performance was greatly enhanced by beta-adrenergic agonists, and meat tenderness from treated animals was classified as intermediate. Furthermore, meat color was not altered by beta-agonist supplementation.     

The effect of roasted soybeans in the diet of feedlot steers and Synovex-S ear implants on carcass characteristics and estimated composition.

Beef steer carcasses from three 2 x 2 factorial feeding experiments (Exp. 1, 20 carcasses; Exp. 2 and 3, 19 carcasses each) were evaluated to study the influence of supplementing with roasted soybeans (RSB; 127 degrees C for 10 min) vs soybean meal (SBM) and implanting with the estrogenic growth promoter Synovex-S (SYN, 20 mg estradiol benzoate and 200 mg progesterone) on carcass merit, composition of dissected 9-10-11th rib section, estimated edible carcass composition, and cooking characteristics of strip loin steaks. In all experiments, steers were fed diets consisting of 15% corn silage, 15% orchardgrass silage, and 70% corn-based concentrate. There were no treatment interactions found in this study. Final BW averaged 480.4, 498.5, and 500.7 kg for Exp. 1, 2, and 3, respectively, and hot carcass weights averaged 288.4, 296.4, and 309.1 kg. Across experiments, hot carcass weight was 8.3 kg less (P < .03) for RSB steers than for SBM steers. Fat weight (P < .01) and percentage of fat (P < .01) were less and percentage of bone (P < .04) was greater in the 9-10-11th rib section of RSB steers than of SBM steers. Estimated percentage of fat (P < .02) was less and percentage of bone (P < .04) was greater in edible carcass of RSB steers than in that of SBM steers. Total 9-10-11th rib section weight tended to be less for RSB steers (P < .08) than for SBM steers. Carcass merit measurements were not affected (P > .10) by supplement, but numerically the percentage of kidney, pelvic, and heart fat was 11% greater for RSB steers than for SBM steers in Exp. 2 and 3. Final BW and carcass weight were 38.7 and 22.6 kg greater (P < .01), respectively, for SYN-implanted steers than for steers not implanted. Longissimus muscle area was greater (P < .01), percentage of kidney, pelvic, and heart fat (P < .02) was less, USDA quality grade tended to be less (P < .09), and shear force of strip loin was greater (P < .01) for SYN-implanted steers than for steers not implanted. The 9-10-11th rib section and estimated carcass compositions were not different (P > .10) between SYN-implanted steers and steers not implanted but reflected a somewhat leaner carcass. The authors conclude from this study that in feedlot steers, either implanted or not implanted, there is no benefit from supplementing with RSB in place of SBM, and that the use of RSB in place of SBM in feedlot diets may reduce the amount of edible carcass.     

Effects of the beta-adrenergic agonist L644,969 on muscle protein turnover, endogenous proteinase activities, and meat tenderness in steers.

Eight MARC III composite (1/4 Hereford, 1/4 Angus, 1/4 Pinzgauer, and 1/4 Red Poll) steers weighing approximately 350 kg were fed 0 or 3 ppm of the beta-adrenergic agonist L644,969 (Merck Sharp and Dohme Laboratories, Rahway, NJ) for 6 wk in a high-concentrate diet. Feed efficiency was higher (P less than .05) in beta-adrenergic agonist-fed steers at 1, 3, 5, and 6 wk on trial. Average daily gain was greater (P less than .05) in beta-adrenergic agonist-fed steers at 3, 5, and 6 wk on treatment. Fractional degradation rate (percentage/day) of skeletal muscle myofibrillar protein was 27.1% lower (P less than .05) in beta-adrenergic agonist-fed steers at 3 wk on trial. Fractional accretion rate (percentage/day) of skeletal muscle myofibrillar protein in beta-adrenergic agonist-fed steers was higher (P less than .05) at 1, 3, 5, and 6 wk on trial. The beta-adrenergic agonist-fed steers had heavier (P less than .05) carcasses (9.6%), larger (P less than .05) longissimus muscle areas (24.3%), and lower (P less than .05) USDA yield grades (43.8%). Marbling degree, USDA quality grade, kidney, pelvic, and heart fat percentage, and 12th rib fat thickness were not different (P greater than .05). Calpastatin activity was higher (P less than .05) in muscle from the beta-adrenergic agonist-fed steers at 0 and 7 d postmortem. There were no differences (P greater than .05) in mu- or m-calpain or in cathepsins B or B+L or cystatin(s) between beta-adrenergic agonist-fed and control steers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth, development, and carcass composition in five genotypes of swine.

An experiment with 127 barrows representing five genotypes, 1) H x HD, 2) SYN, 3) HD x L[YD], 4) L x YD, and 5) Y x L (H = Hampshire, D = Duroc, SYN = synthetic terminal sire line, L = Landrace, and Y = Yorkshire), was conducted to evaluate growth and development of swine from 59 to 127 kg live weight. Animals were allowed ad libitum access to a pelleted finishing diet containing 18.5% CP, .95% lysine, and 10.5% fat, with an energy density of 3,594 kcal of ME/kg. Pigs were serially slaughtered at either 59, 100, 114, or 127 kg live BW. After slaughter, carcasses were chilled and backfat was measured at four locations. The right side of each carcass was fabricated into primal cuts of ham, loin, Boston Butt, picnic, and belly. Composition of each primal cut was determined by physical dissection into lean, fat, bone, and skin. Estimated allometric growth coefficients for carcass length, carcass weight, and longissimus muscle area relative to BW; carcass lean, fat, bone, and skin relative to both BW and carcass weight; and lean in each of the primal cuts relative to total carcass lean did not differ (P greater than .05) among genotypes. Relative to BW, the pooled growth coefficient(s) for carcass weight was (were) greater (P less than .001) than unity, whereas those for carcass length, longissimus muscle area, and backfat at first rib were smaller (P less than .001) than unity. Those for other backfat measurements were close to 1.00. Relative to either BW or carcass weight, the pooled coefficient(s) for fat was (were) greater (P less than .001) than unity, whereas those for lean, bone, and skin were smaller (P less than .001) than unity. Growth of lean, backfat, bone, and skin in the carcass were nearly linearly associated with increases in BW. The increase in fat weight was curvilinear as the pig grew and was accelerated in later growth stages, indicating that carcass fat percentage increased with increased BW.     

Physical and chemical components of the empty body during compensatory growth in beef steers

The composition of carcass and noncarcass tissue growth was quantified by serial slaughter of 26 Angus x Hereford crossbred steers (initial age and weight 289 +/- 4 d and 245 +/- 4 kg) during continuous growth (CON) or compensatory growth (CG) after a period of growth restriction (.4 kg/d) from 245 to 325 kg BW. All steers were fed a 70% concentrate diet at ad libitum or restricted levels. Homogenized samples of 9-10-11th rib and noncarcass tissues were analyzed for nitrogen, fat, ash, and moisture. Growth rate from 325 to 500 kg BW was 1.54 and 1.16 kg/d for CG and CON steers. The weight of gut fill in CG steers was 10.8 kg less (P less than .05) before realimentation and 8.8 kg more (P less than .10) at 500 kg BW than in CON steers. The allometric accretive rates for carcass chemical components relative to the empty body were not affected by treatment. However, the accretive rates for CG steers were greater (P less than .01) for noncarcass protein (.821 vs .265), noncarcass water (.861 vs .507), and empty-body protein (.835 vs. .601) than for CON steers. Final empty-body fat was lower (P less than .001; 24.2 vs 32.4%) and empty-body protein higher (P less than .001; 16.6 vs 14.8%) in CG steers than in CON steers. Consequently, net energy requirements for growth (NEg) were approximately 18% lower for CG steers. We conclude that reduced NEg requirements and changes in gut fill accounted for most of the compensatory growth response exhibited in these steers.     

Genetic and phenotypic relationships of serum leptin concentration with performance, efficiency of gain, and carcass merit of feedlot cattle

Leptin is the hormone product of the obese gene that is synthesized and predominantly expressed by adipocytes. This study estimated the genetic variation in serum leptin concentration and evaluated the genetic and phenotypic relationships of serum leptin concentration with performance, efficiency of gain, and carcass merit. There were 464 steers with records for serum leptin concentration, performance, and efficiency of gain and 381 steers with records for carcass traits. The analyses included a total of 813 steers, including those without phenotypic records. Phenotypic and genetic parameter estimates were obtained using SAS and ASREML, respectively. Serum leptin concentration was moderately heritable (h2 = 0.34 +/- 0.13) and averaged 13.91 (SD = 5.74) ng/mL. Sire breed differences in serum leptin concentration correlated well with breed differences in body composition. Specifically, the serum leptin concentration was 20% greater in Angus-sired steers compared with Charolais-sired steers (P < 0.001). Consequently, ultrasound backfat (27%), carcass 12th-rib fat (31%), ultrasound marbling (14%), and carcass marbling (15%) were less in Charolais- than Angus-sired steers (P < 0.001). Conversely, carcass LM area (P = 0.05) and carcass lean meat yield (P < 0.001) were greater in Charolais- compared with Angus-sired steers. Steers with greater serum leptin concentration also had greater DMI (P < 0.001), greater residual feed intake (P = 0.04), and partial efficiency of growth (P = 0.01), but did not differ in feed conversion ratio (P > 0.10). Serum leptin concentration was correlated phenotypically with ultrasound backfat (r = 0.41; P < 0.001), carcass 12th-rib fat (r = 0.42; P < 0.001), ultrasound marbling (r = 0.25; P < 0.01), carcass marbling (r = 0.28; P < 0.01), ultrasound LM area (r = -0.19; P < 0.01), carcass LM area (r = -0.17; P < 0.05), lean meat yield (r = -0.38; P < 0.001), and yield grade (r = 0.32; P < 0.001). The corresponding genetic correlations were generally greater than the phenotypic correlations and included ultrasound backfat (r = 0.76 +/- 0.19), carcass 12th-rib fat (r = 0.54 +/- 0.23), ultrasound marbling (r = 0.27 +/- 0.22), carcass marbling (r = 0.76 +/- 0.21), ultrasound LM area (r = -0.71 +/- 0.19), carcass LM area (r = -0.75 +/- 0.20), lean meat yield (r = -0.59 +/- 0.22), and yield grade (r = 0.39 +/- 0.26). Serum leptin concentration can be a valuable tool that can be incorporated into appropriate selection programs to favorably improve the carcass merit of cattle.     

Recombinant porcine somatotropin alters performance and carcass characteristics of heavyweight swine and swine fed alternative feedstuffs

The efficacy of recombinantly derived porcine somatotropin (rpST) in improving the performance and carcass characteristics of heavyweight finishing pigs was determined. In Study 1, 36 pigs were killed for determination of initial carcass composition at 102 kg, and 36 pigs each were given 0, 1.5, 3, 6, or 9 mg of rpST/d from 102 to 136 kg live weight. Corn-soybean meal diets fed contained 19.8% CP and greater than 1% lysine. Study 2 tested the effects of 3 mg/d on pigs for 4 wk from 84 kg BW fed a corn-soybean meal or a triticale-barley-peas diet. Performance variables (ADG, average daily feed intake [ADFI], and feed efficiency [FE]) were measured weekly. Treatment with rpST increased (P less than .01) ADG and FE and decreased (P less than .01) ADFI in both studies. In Study 1, leaf fat, backfat thickness, belly thickness, and carcass fat were all decreased (P less than .01) linearly by rpST. Loin eye area (LEA), total trimmed lean, and total protein content were increased quadratically (P less than .01). At the 3-mg dose, ADFI, ADG, and FE were 87, 130, and 137% of control, and LEA, backfat, total protein gain, and total fat gain were 107, 80, 136, and 52% of control. Loin eye area was not increased (P greater than .05) in the pigs in Study 2; however, backfat thickness was reduced 16% by rpST (P less than .01). The effects of rpST were the same on both dietary regimens (P greater than .05). These studies demonstrate the effectiveness of rpST in increasing ADG and carcass leanness and improving FE in heavyweight pigs and in pigs fed alternative feedstuffs.     

Growth performance and carcass traits of pigs subjected to marginal dietary restrictions during the grower phase.

Sixty-four individually housed pigs were used to investigate the effect of amino acid content of finisher diets on growth performance of pigs subjected to marginal dietary amino acid restrictions (80% of the 1988 NRC lysine recommendation) during the grower phase. In each of the two trials, low- and high-amino-acid grower diets (.421 and .765 g lysine/MJ DE, respectively) and four finisher diets (.421, .516, .612, and .707 g lysine/MJ DE) were randomly assigned within sex to 16 gilts and 16 castrated males weighing 23.0 +/- 2.0 kg in a 2 x 4 factorial arrangement of treatments. The average weight of pigs after a completion of diet change was 50.4 +/- 2.1 kg. All pigs were slaughtered at an average weight of 105.2 +/- 4.1 kg. Ultrasound backfat thickness was measured at the time of diet change and before slaughter. Pigs were allowed ad libitum access to feed and water. During the grower phase, pigs fed the high-amino-acid diet grew faster (P < .001) and more efficiently (P < .001) and had less ultrasound backfat (P < .001) than those fed the low-amino-acid diet. The grower diet had no effect on weight gain during the finisher phase. Consequently, pigs fed the high-amino-acid grower diet had better overall weight gain (P < .01) than those fed the low-amino-acid diet. The rate of lean accretion was, however, similar between the two groups of pigs. Furthermore, pigs fed the low-amino-acid grower diet seemed to have better carcass quality, as indicated by less ultrasound backfat (P < .01) and larger carcass longissimus muscle area (P < .05). Average and 10th rib carcass backfat decreased linearly (P < or = .05) and lean accretion rate improved linearly (P < .05) as the amino acid content of finisher diets increased, but there was no grower x finisher diet interaction in these and other response criteria. Although no evidence of compensatory weight gain was observed, it is possible that compensatory lean tissue growth may have occurred in pigs subjected to early amino acid restrictions at the expense of fatty tissue growth.     

Additive and nonadditive differences in postweaning growth and carcass characteristics of Devon, Hereford, and reciprocal-cross steers.

Postweaning growth and carcass characters of 110 steers from a complete two-breed diallel of the Devon and Hereford breeds were examined under two environments. Additive and nonadditive effects were estimated using linear contrasts for several growth and carcass traits. Steers from each of the four breed groups were grown postweaning to slaughter in high- and low-nutrition environments. Weights were recorded every 2 mo. At slaughter, hot carcass weight, longissimus muscle area, kidney and channel fat, and subcutaneous fat at nine sites were measured. Heterosis for postweaning growth rate was 3.9% (P less than .01) and for slaughter weight 5.0% (P less than .01). Within the low-nutrition environment during periods of slow and fast growth, the Devons and Herefords performed differently. The growth rate of the steers differed in the two environments; however, heterosis for slaughter weight was of the same magnitude in both environments. No differences existed between the straightbreds or between the reciprocal crosses for slaughter weight. Crossbred carcasses were 7.4% heavier (P less than .01) than the straightbred carcasses; however, this effect was removed after adjustment for differences in slaughter weight. Heterosis for longissimus muscle area and carcass fatness were not significant after adjusting for carcass weight. Additive differences occurred for carcass traits. Devon carcasses had more kidney and channel fat (P less than .05) at a constant hot carcass weight and differences occurred in the partitioning of fat within the subcutaneous depot. No significant maternal effects were observed for the carcass traits measured. Crossbreeding increased carcass weight without altering composition, and relative performance was not affected by the diverse environments.     

Grazing methods and stocking rates for direct-seeded alfalfa pastures: I. Plant productivity and animal performance

A 4-yr study was conducted to determine the effects of two grazing methods (GM) at two stocking rates (SR) on alfalfa pasture plant productivity and animal performance and to ascertain the effect of grazing systems on subsequent performance of steers fed a high-concentrate diet. Eight pasture plots (.76 ha) were seeded in 1988 with alfalfa (Medicago sativa L. var. WL225) and divided into two blocks of four pastures each. Grazing methods consisted of a traditional four-paddock or an intensive 13-paddock system. Pastures were managed to allow a 36-d rest period with an average grazing season of 110 d. The low and high SR were 5.9 vs 11.7, 5.3 vs 10.5, 5.3 vs 7.9, and 5.3 vs 7.9 steers/ha for years 1989 to 1992, respectively. Following the grazing season, steers were placed in a feedlot and fed a high-concentrate diet (81% high-moisture corn, 14% corn silage, 5% protein-mineral supplement) for an average of 211 d. There was no effect of GM on herbage mass, pasture phase ADG, or live weight gain/hectare. Increasing the number of paddocks was beneficial when herbage mass was limited and stocking rate was above 7.9 steers/ha. Increasing SR above 7.9 steers/ha decreased herbage mass and pasture-phase ADG. As forage allowance increased, pasture-phase ADG increased quadratically (R2 = .82, P < .001), reached a plateau, and then decreased. Previous grazing system did not influence the performance of steers in the feedlot or their carcass characteristics. Optimum SR is dependent on herbage mass produced.     

Alterations in postmortem degradation of myofibrillar proteins in muscle of lambs fed a beta-adrenergic agonist

Dietary administration of 4 ppm of the beta-agonist L-644,969 (Merck Sharpe and Dohme Research Laboratories) to finishing lambs induced a decrease (10 to 14%, P less than .05) in extractable calpain I activity in the longissimus muscle (LD) at death (d 0). At 4 d postmortem (d 4), extractable calpain I levels in the LD of both control and treated lambs were reduced (P less than .001) from those present at d 0, but the extractable activity in the LD was reduced to a greater extent in control than in treated lambs. Calpain II activity was increased 42% (P less than .005) in LD of treated lambs; however, no significant differences were observed between d 0 and d 4 calpain II activity within treated or control LD samples (P greater than .1). Calpastatin activity was higher in the LD of treated lambs (74% on d 0, P less than .001 and 430% on d 4, P less than .001) than in the LD of control lambs. Measurable cathepsin B activity was decreased (29% on d 0, P less than .05) and measurable cathepsin H activity was increased (10% on d 0, P less than .05 and 10% on d 4, P less than .05) in the LD of treated lambs compared with controls. On d 2, 4 and 6 postmortem, degradation in myofibrils isolated from the LD was lower for treated than for control lambs. Warner-Bratzler shear values for loin chops from treated lambs were higher on both d 3 (111%) and 6 (108%) postmortem than for chops from control lambs (P less than .001). L-644,969-induced decreases in muscle proteolytic capacity may limit postmortem myofibril degradation and contribute to the reduced tenderness observed. This decreased proteolytic capacity may contribute to increased muscularity of L-644,969-treated lambs.     

Effect of days fed, carcass grade traits, and subcutaneous fat removal on postmortem muscle characteristics and beef palatability.

Angus x Hereford steers (n = 48) similar in frame size and in muscle thickness were allotted to eight groups (n = 6) of similar mean live weight for serial slaughter at 28-d intervals (0 to 196 d). Except for d-0 steers, which served as grass-fed controls, all steers were fed a high-concentrate diet during the finishing period. Upon slaughter, one side of each carcass was trimmed of subcutaneous fat in the wholesale rib region. Postmortem longissimus muscle (LM) temperature was monitored for each side during the 24-h chilling period. After quality and yield grade data were collected, rib steaks were removed and aged (7 d) and sensory traits of the steaks were evaluated. Most carcass grade traits increased linearly (P less than .01) with days on feed, whereas most sensory panel variables and marbling increased curvilinearly (P less than .05). Generally, after 56 d on feed, carcasses chilled at slower rates (P less than .05) with increased days fed. Taste panel tenderness, amount of perceived connective tissue, and shear force values peaked at 112 d and were slightly less desirable for cattle fed longer than 112 d (quadratic term, P less than .01). Postmortem muscle temperature at 2.5 h was the chilling time most highly correlated with tenderness values among untrimmed sides. Correlations for shear force with 2.5-h LM temperature, marbling score, days fed, fat thickness, and carcass weight were -.63, -.61, -.56, -.55, and -.53, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and metabolism in somatotropin-treated steers: II. Carcass and noncarcass tissue components and chemical composition

Carcass and noncarcass tissue compositional characteristics were determined in growing Hereford steers treated with daily subcutaneous injections (20.6 mg/d) of recombinantly derived bovine somatotropin (rBST) for 112 d. For carcass primal cuts, weights and rates of gain of bone, lean and total fat and site of fat deposition were not significantly affected by rBST treatments with the exception of a few tissues (loin total weight, flank total and lean weight and shank total weight). Lean to fat ratios, however, were greater (P less than .1) for the loin, flank, chuck and brisket. Weights and growth of individual muscles from the hindquarter were not affected by rBST administration. Weights and(or) average daily gains of the liver, kidneys, lungs and trachea and head were greater (P less than .05) in rBST-treated animals. Weights and (or) average daily gains were greater (P less than .1) in rBST-treated steers for water in the total body and carcass, for CP in the total body and noncarcass, and for ash in the total body, carcass and noncarcass. Ratios of CP to ether-extractable fat in the total body were greater (P less than .1) in rBST steers. These data indicate that rBST modified carcass lean and fat composition in cattle, but responses were modest compared to effects of somatotropin treatment of swine.     

Age of calf at weaning of spring-calving beef cows and the effect on cow and calf performance and production economics

Over a 5-yr period, spring-calving cows were used in a carry-over design experiment to evaluate effects of calf age at weaning on cow and calf performance and production economics. Weaning management groups were early (n = 60, calf age 150 d, EW), traditional (n = 60, calf age 210 d, NW), and late (n = 60, calf age 270 d, LW). Cow body condition score (BCS) and weights at the last weaning date were different (P < .05) for EW (5.8, 583 kg), NW (5.5, 560 kg), and LW (5.2, 541 kg) management groups. Pregnancy rates among groups were similar. Days on feed for groups differed (P = .001) and was 247 for EW, 204 for NW, and 164 d for LW steers. Average daily gain in the feedlot differed (P = .01) among groups and averaged 1.5 kg for LW, 1.4 kg for NW, and 1.3 kg for EW steers. Dry matter intake while steers were in the feedlot was greater (P = .001) for LW than for NW and EW calves. Hot carcass weight was greater (P = .01) for EW (328 kg) and NW (332 kg) calves than for LW (321 kg) steers, and fat depth was greater (P = .05) for EW and NW steers than for LW steers. When carcass data for the NW and LW steers were adjusted to the fat depth of EW steers, carcass characteristics among groups were similar. Net income per steer at slaughter for the feedlot phase was greater (P < .001) for the EW ($75.36) and NW ($62.16) steers than for the LW ($10.09) steers. Again, when carcass data for the NW and LW steers were adjusted to the same fat depth of the EW steers, net income differences among groups were reduced. Replacement heifers were developed in a drylot and costs were higher (P < .001) for the EW than for NW and LW heifers. Annual cow costs were greater (P < .10) for the LW ($443.45) than for the EW ($410.09) and NW ($421.35) groups. Break-even for each system on a steer financial basis was not different between the NW and LW groups, and both the NW and LW groups had lower (P = .08) break-evens than the EW group. Age of the calf at weaning affects cow weight and BCS. Net income in each system is influenced by cow costs, month of the year that steer calves are purchased into the feedlot and finished steers are sold, month of the year cull cows are marketed, and replacement heifer development costs.     

Effect of degree of corn processing on urinary nitrogen composition, serum metabolite and insulin profiles, and performance by finishing steers

Two experiments were conducted to determine the effect of degree of corn processing on urinary ammonia and urea N concentrations, serum metabolite and insulin concentrations, and feedlot performance of steers. Corn was processed by either dry rolling to .54 kg/L bulk density (DR42; 42 lb/bushel) or steam flaking to a bulk density of .36 or .26 kg/L (28 [SF28] and 20 [SF20] lb/bushel, respectively). Degrees of processing were selected to generate final products with 25, 50, or 75% enzymatically available starch. Available starch, expressed as a percentage of total starch for DR42, SF28, and SF20, averaged 24.5, 56.4, and 81.1% in Exp. 1 and 22.4, 60.1, and 80.1% in Exp. 2. In Exp. 1, 29 steers were housed in individual outdoor pens and adapted to a 90% concentrate diet over 21 d. Whole blood and urine were collected before feeding and at 4 and 8 h after feeding on d 0, 7, 14, 21, 28, 84, and 140. Daily DMI decreased linearly (P < .03) as degree of processing increased, whereas water intake did not differ (P > .42) among treatments. Average daily gain, ADG:DMI, and hot carcass weight responded quadratically (P < .04) to an increasing degree of processing. Urinary ammonia and urea N concentrations were not influenced (P > .30) by degree of processing. Whole blood packed cell volume, serum glucose, creatinine, D(-)-lactate, L(+)-lactate, and lactate dehydrogenase activity did not differ (P > .15) among treatments. For insulin data, ME intake on the day of sample collection was evaluated as a covariate. On d 28, serum insulin (2.49, 2.95, and 1.80+/-.33 ng/mL) responded quadratically (P = .04) as degree of processing increased. Serum insulin did not differ (P = .52) on d 84, whereas insulin (5.77, 7.51, and 4.12+/-.98 ng/mL) responded quadratically (P = .02) on d 140. In Exp. 2,216 steers were blocked by BW into two blocks (18 pens; 12 steers/pen) and assigned to the same treatments used in Exp. 1. Daily DMI and carcass weight responded quadratically (P < .05), whereas ADG and ADG:DMI increased linearly (P < .04) with increasing degree of processing. Results suggest that the degree of corn processing influences serum insulin concentrations of feedlot steers; however, serum metabolites, urinary nitrogen composition, and carcass characteristics were generally not affected by degree of corn processing.     

Physiological and pathological effects of feeding high levels of magnesium to steers

The effects of feeding high levels of Mg were evaluated in a 130-d study with 24 steers. Six steers were allotted to each of four diets supplemented with MgO to attain .3, 1.4, 2.5 or 4.7% Mg, DM basis. Chromic oxide was used as digesta marker; fecal grab samples were collected once daily during nine consecutive 10-d periods. Steers fed 2.5 and 4.7% Mg refused some feed during the study, so their respective dietary Mg intakes were 2.4 and 3.7% (DM basis). Severe diarrhea and a lethargic appearance were observed in steers fed the two higher Mg levels. Fecal DM and apparent DM digestibility decreased linearly (P less than .01) with increased dietary Mg. Apparent Mg absorption (g/d) increased linearly (P les than .01) and apparent Ca and P absorption (g/d) decreased linearly (P less than .01) with addition of Mg to the diet. Increasing dietary Mg linearly elevated blood serum and erythrocyte Mg (P less than .01; P less than .05, respectively) and serum inorganic P (P less than .05) and linearly decreased serum Ca (P less than .01). Magnesium concentration in liver, kidney, skeletal muscle and rib-bone and P in skeletal muscle all increased linearly (P less than .05) with dietary Mg. Increasing dietary Mg in the steers caused a progressive degeneration of the stratified squamous epithelium of rumen papillae. A progressively more serious Mg toxicosis condition developed over time in steers fed diets containing 2.4 and 4.7% Mg.     

Effects of energy intake, implantation, and subcutaneous fat end point on feedlot steer performance and carcass composition

The purpose of this experiment was to evaluate the effects of energy intake, implantation, and fat end point on feedlot performance and carcass composition of steers. Three hundred eighty-four yearling crossbred steers (368 +/- 23.1 kg) were allotted in a completely randomized design. Treatments were arranged in a 2 x 3 x 2 factorial experiment. Main effect factors were two levels of intake, three implant strategies, and two compositional fat end points at slaughter. The levels of intake were ad libitum (AL) and restricted (RS) intake (90% ad libitum). The three implant strategies were Revalor-S (REV) (120 mg trenbolone acetate, 24 mg estradiol), Synovex-Plus (SYN) (200 mg trenbolone acetate, 28 mg estradiol benzoate), and no implant (control). The compositional target end points were 1.0 and 1.4 cm s.c. fat cover over the 12th and 13th rib. Restricted-intake steers consumed 9.2% less (P < .01) DM than AL steers. Ad libitum-intake steers gained weight 15.5% more rapidly (P < .01) than RS-intake steers. Steers implanted with REV tended (P < .07) to gain faster than SYN steers, who in turn gained 15.2% more (P < .01) than control steers. Ad libitum-intake steers were 4.8% more (P < .01) efficient than RS steers. Steers fed to a targeted 1.4 cm s.c. backfat cover were 2.9% less (P < .05) efficient than steers fed to 1.0 cm, and steers implanted with either REV or SYN had similar (P = .47) feed efficiencies, whereas control steers had lower (P < .01) feed efficiencies. Steers fed to a targeted compositional fat end point of 1.4 cm had 1.3% higher (P < .01) dressing percentage (DP) than steers fed to 1.0 cm. Control and SYN steers had similar (P = .13) DP; however, REV steers had 6.1% greater (P < .01) DP than SYN steers. Steers fed to 1.4 cm s.c. fat end point had higher (P < .01) numerical yield grades than steers fed to 1.0 cm (3.34 vs 2.71). There was an interaction (P < .01) for intake level and implant for marbling score. Marbling scores were lower (P < .05) for RS x SYN and AL x REV than in other treatments. Steers on the RS x REV treatment were intermediate in marbling to all treatments except AL control, which was higher (P < .01) than RS x SYN, AL x REV, and RS x REV. No interaction for dry matter intake level and anabolic implants was observed for growth performance. The depression in carcass quality resulting from implanting is reduced as backfat increases from 1.0 to 1.4 cm at slaughter.     

The effect of zeranol on live weight gain, feed intake and carcass composition of steers during compensatory growth

To evaluate the effect of zeranol implants in steers on compensatory ++growth, 80 steer calves (9 mo of age; 200 kg) were fed at two feeding levels (RO = 9.2 MJ ME/kg DM; R1 = 6.9 MJ ME/kg DM) for 119 d (Period 1). During Period 2, steers were full-fed to 400 kg BW with (Z1) or without (ZO) zeranol implants. Ten steers were slaughtered at the end of Period 1 to estimate carcass composition. Differences of 100 kg in BW were achieved by restriction in Period 1. Subsequent to restriction, cumulative ADG remained greater (P less than .05) up to the 24th wk of recuperation and implants increased (P less than .001) BW gain by 31% and 24% for RO and R1, respectively. The average daily energy intake (ME/W(.75) in Period 2 was similar for all treatments. Feed conversion was improved by 21.5% (P less than .05) by implants. At the end of Period 2 the R1ZO had 8.6 kg less muscle (P less than .001), 2.9 kg less bone (P less than .001) and 5.9 kg more fat (P less than .05) than the ROZO. In comparison, the carcasses of the implanted animals did not show significant differences (P greater than .05) due to restriction. Carcass daily gains were increased by previous restriction (P less than .01) and implants (P less than .05). Zeranol increased daily live weight gain and feed conversion in animals in continuous growth as well as in those observed in compensatory growth an tended to eliminate a tendency for higher content of fat in carcasses of nonimplanted animals making compensatory growth.     

Failure of photoperiod to alter body growth and carcass composition in beef steers

In each of two experiments, 70 crossbred steers were blocked by BW and assigned to initial slaughter groups or to treatments in a 2 x 2 design. In Exp. 1, treatments were 168 d of photoperiod (8 h of light [L]:16 h of dark [D] or 16L:8D) and plane of nutrition (high energy [HPN] or low energy [LPN]). On d -22, 67 and 155, blood was sampled every 20 min for 8 h. Relative to LPN, HPN increased (P less than .01) ADG by 28%, carcass weight by 26% and accretion of carcass fat by 109% and carcass protein by 20%. On d 155, compared with LPN, HPN increased (P less than .01) serum insulin (INS; 1.09 vs .64 ng/ml) and lowered (P less than .05) growth hormone (GH; 2.14 vs 3.70 ng/ml), but prolactin was not affected. Photoperiod did not affect BW gains, carcass composition or serum hormones. In Exp. 2, treatments were 113 d of photoperiod (8L:16D or 16L:8D) and Synovex-S implant (presence [IMP] or absence [NONIMP]). On d 93, blood was sampled every 30 min for 10 h. Relative to NONIMP, IMP increased (P less than .01) ADG by 12% and accretion of carcass protein by 16%. Implants did not affect carcass weight or accretion of fat. Compared with NONIMP, IMP increased (P less than .05) GH (3.16 vs 2.39 ng/ml) and INS (.68 vs .46 ng/ml) but did not affect PRL. Photoperiod did not affect BW gain, carcass composition or serum hormones. We conclude that photoperiod fails to influence growth and carcass composition of steers.