The effects of dietary crude protein level on rate, efficiency and composition of gain of growing beef bulls

Two experiments were conducted to evaluate the effects of dietary CP level on rate, efficiency and composition of gain of growing beef bulls. In Exp. 1, 59 bulls (333 +/- 15.8 kg) were used. Eleven bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-10-11 rib section chemical analyses), and remaining bulls were assigned to treatment diets containing 10, 12 or 14% dietary CP. Bulls fed the 10% CP diet grew slower (P less than .05) than bulls fed the 12 or 14% CP diets, although dry matter intake and feed-to-gain ratio did not differ. Bulls fed the 12% CP diet had fatter carcasses (P less than .05) than bulls fed the 10 or 14% CP diets and had greater daily fat accretion than bulls fed the 10% CP diet. In Exp. 2, 60 bulls (318 +/- 9.0 kg) were used. Bulls were assigned to initial slaughter (n = 6) or to one of three dietary treatments, 10, 12 or 14% CP, and were slaughtered after feeding for 66, 136 or 202 d (n = 6 . treatment -1 . slaughter time -1). Bulls fed 10% CP diets had lower (P less than .05) rates of carcass protein accretion during d 0 to 136 and d 0 to 202. Carcass fat gain was similar among treatments over the entire experiment, although bulls fed the 14% CP diet gained more fat during d 0 to 136 than bulls fed the other treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and hormonal response of intact and castrate male cattle to trenbolone acetate and estradiol

Effects of castration and anabolic implants on weight gain, rib soft tissue composition and serum hormones were studied in cattle using a completely random design with a 2 x 2 factorial arrangement. Half of 16 bulls and 16 steers (Angus or Angus x Brahman) aged 9 mo and weighing 290 kg were treated with an implant (200 mg trenbolone acetate and 24 mg estradiol). Half of each group were not treated with an implant. A growing diet was fed for 95 d and half the animals in each group were slaughtered. Animals in the treated groups were reimplanted with trenbolone acetate and fed a finishing diet for 84 d and slaughtered. Percentage dry matter, fat and protein were determined on soft tissue from the 9-10-11th rib. Two blood samples were collected from each animal every 2 wk. Serum was assayed for five hormones. During the growing phase, untreated and treated bulls and treated steers gained more weight and had leaner rib sections that untreated steers (P less than .05); after the finishing phase, there were no differences among groups. Untreated steers had lower insulin-like growth factor (IGF-I) and higher cortisol concentrations during both phases of growth than untreated bulls did (P less than .05). Treatment with implants increased IGF-I concentrations in steers during both phases and reduced cortisol during the finishing phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of bovine growth hormone and thyroxine on growth rate and carcass measurements in lambs

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

Effect of testosterone propionate on performance and carcass characteristics of heifers and cows

Two experiments were conducted to evaluate the effect of testosterone on growth and composition of cattle. In the first experiment, crossbred yearling heifers (n = 48) were assigned to four treatments: 1) control (no implant), 2) Synovex-H implants on d 1 and 84, 3) one testosterone propionate implant administered on d 1 and a second on d 84 and 4) two testosterone propionate implants administered on d 1. Heifers were fed a high-energy diet for the 157-d study. Implanting with the high-testosterone treatment improved (P less than .05) daily gain and feed efficiency compared with the other treatments. Marbling score was reduced (P less than .05) with the high-testosterone treatment. In Exp. 2, mature cows (n = 36) were assigned to one of three feeding periods (0, 42, or 84 d) with the cows fed 42 or 84 d subdivided into two groups (implanted with testosterone propionate or nonimplanted control). Cows were fed a high-energy diet and slaughtered at the end of each feeding period. Testosterone did not influence (P greater than .05) feedlot performance. Increased time on feed reduced (P less than .01) daily gain (live weight basis) and feed efficiency but did not influence feed intake. Testosterone treatment had little influence on the fat and moisture contents of the carcass soft tissue or on the palatability characteristics of loin steaks. Time on feed increased lean muscle mass and carcass fat (P less than .05). Sensory traits were improved at 42 d on feed (P less than .05), but no further sensory improvement was observed at 84 d.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth performance and carcass composition of lambs infused for 28 days with a growth hormone-releasing factor analogue.

A human growth hormone-releasing factor analogue, [DesNH2Tyr1,D-Ala2,Ala15]hGRF(1-29)NH2 (GRF-A), was infused s.c. into lambs for 28 d to determine its effects on growth performance and carcass composition. Twenty crossbred wethers weighing 47.0 +/- .5 kg were implanted with 7-d osmotic minipumps at weekly intervals. Minipumps contained either vehicle (dimethyl sulfoxide:H2O, 1:1) or GRF-A, released at a rate of 208 pmol (or .7 micrograms).h-1.kg-1. During the infusion period, plasma GH levels were increased (P less than .01) in GRF-A-treated wethers compared with control wethers (15.0 vs 9.3 ng/ml) and were higher on days that closely followed minipump implantation. Plasma IGF-I and hepatic IGF-I RNA concentrations were similar in lambs of both groups. Analogue treatment improved feed conversion (4.9 vs 5.8 kg dry matter/kg gain, P less than .05), increased average daily gain (.35 vs .30 kg, P = .05) and had no effect on feed intake, wool growth and body, carcass, selected organ and pituitary weights. Carcasses from GRF-A-infused lambs had less adjusted fat depth, a lower percentage of fat and a higher percentage of protein (P less than .05) than carcasses from control lambs. Magnitude of most effects of GRF-A on carcass measurements were correlated with the mean GH level that a lamb had during the infusion period. In conclusion, s.c. infusion of GRF-A improved feed utilization and altered carcass composition of feeder lambs in a relatively short period of time (28 d).     

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.     

Relationships among serum characteristics and performance and carcass traits in growing pigs

Twelve blood serum components were determined on 78 barrows and 66 gilts, serially slaughtered at six age groups, starting at 69 d, at 2-wk intervals. One-half of the animals were fed ad libitum and one-half were fed "time restricted". Partial correlations between production and carcass traits and serum components were calculated from the residuals of the least-squares analysis. Calcium, serum protein and albumin were highly (P less than .01) correlated with several production and carcass traits. Creatinine was positively correlated (P less than .05) with backfat, loin fat, and percent dissected muscle and bone. Alkaline phosphatase showed a positive relationship with average daily gain (P less than .05) and percent dissected bone (P less than .01). A stepwise regression analysis was used to examine simultaneously the relative predictive value of the blood serum components. The nitrogenous compounds, which included albumin, total protein, urea and creatinine, were the most important predictors of performance (avg daily gain, feed conversion) and carcass composition. However, most of the serum components were not related to the performance and carcass composition traits.     

Growth traits and composition of two- and three-way-cross intact male progeny of Bos taurus and Bos indicus X Bos taurus dams

Feedlot traits, carcass traits and distribution of commercial cuts of crossbred intact male progeny (n = 556) from young and mature Hereford, Red Poll, Hereford X Red Poll, Red Poll X Hereford, Angus X Hereford, Angus X Charolais, Brahman X Hereford and Brahman X Angus dams were evaluated. First-calf heifers were bred to Red Angus bulls; Santa Gertrudis sires were used for each cow's second and third breeding seasons. Calves from these young dams were slaughtered at 13 mo. Calves of mature dams were all sired by Limousin bulls and slaughtered at 12 mo. Dam breed was a major source of variation in most bull traits. Progeny of Brahman-cross dams were inferior (P less than .01) in daily gain, final weight, carcass weight and in edible cuts/day of age compared with progeny from Bos taurus dams. Intact male progeny of Angus X Charolais dams ranked highest in longissimus area, cutability, and edible cuts/day of age. The range of dam breed means in percentage of steak, roast, bone-in cuts (chuck short ribs and back ribs), short plate and thin cuts, and lean trim was just over 1%. Greater variation among dam breeds existed in fat measurements. Analyses in which Hereford-Red Poll diallel data for young dams and mature dams were combined showed positive maternal heterosis for dressing percentage (P less than .05), carcass weight (P less than .05), carcass weight/day of age (P less than .05), estimated carcass fat (P less than .05), fat thickness (P less than .01) and marbling score (P less than .01). Reciprocal effects were inconsequential. Results illustrate the importance of dam breed-type effects in formulating breeding strategies for commercial beef herds.     

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)     

Implanting young bulls with zeranol from birth to four slaughter ages: I. Live measurements, behavior, masculinity and carcass characteristics

Seventy-two Simmental bull calves were allotted randomly at birth to either a zeranol (Ralgro) implanted (I) treatment or a nonimplanted control (C) group. At birth, bulls assigned to the I treatment were implanted with 36 mg of zeranol and reimplanted at average intervals of 84 d until slaughter. Calves were weaned at 7.2 mo, preconditioned for 2 wk, and randomly assigned by treatment to slaughter ages of 12.0, 13.8, 15.7 and 17.4 mo and fed an 83% concentrate diet until slaughter. At 7.7 mo and all slaughter ages, live weights and hip heights were similar (P greater than .10), but I bulls had lower (P less than .05) masculinity scores than C bulls. Scrotal circumferences for I bulls were smaller (P less than .05) at 7.7, 12.0, 13.8 and 15.7 mo, but similar (P greater than .10) at 17.4 mo to C bulls. Behavioral observations of passive bunting, mounting attempts, facility rubbing and overall activity were less (P less than .05) for I bulls than C bulls from 12.0 to 13.8 mo but similar (P greater than .10) from 13.8 to 17.4 mo. Aggressive bunting was less (P less than .05) for I bulls during five of the seven observation times for the 12.0-to-13.8-mo period only. Slaughter and carcass weights and dressing percentages were similar (P greater than .10) for I and C bulls. Skeletal maturity and marbling scores, fat thicknesses, yield grades and 9-10-11th rib fat percentages were higher (P less than .05) and lean maturities, forehead hide weights, high dermis thicknesses, femur measurements and 9-10-11th rib bone weights and percentages were lower (P less than .05) for I than C bulls. Rib eye areas and carcass masculinity traits of jump muscle and crest of I bulls were less (P less than .05) at 13.8 mo but reached similar (P greater than .10) development to C bulls at 15.7 mo. Testicle weights of I bulls were lighter (P less than .05) at 12.0, 13.8 and 15.7 mo, but similar (P greater than .10) to C bulls at 17.4 mo. Growth traits (all weights plus hide and femur measurements) and maturation traits (skeletal and lean maturities, marbling scores, fat thicknesses and pizzle eye sizes) increased the most from 12.0 to 13.8 mo and 13.8 to 15.7 mo, respectively. We concluded that implanting young bulls with zeranol from birth to slaughter had minimal effects on live measurements, improved carcass desirability and delayed masculinity and behavioral development.     

Effects of sire growth potential, growing-finishing strategy, and time on feed on performance, composition, and efficiency of steers.

Beef production systems that increase use of unharvested forages and use animals with greater potential for gain affect age and size of animals placed on a finishing regimen. This experiment was conducted to evaluate effects of genetic potential for gain, age at the start of a finishing period, and time on feed on composition, quantity, and quality of beef produced and efficiency of production during finishing. Crossbred cows were bred by AI to Charolais or Line 1 Hereford bulls that represented potentially high (HG) or moderate growth (MG) rates, respectively, to produce spring- or fall-born calves. Steer calves from these matings were placed on an individually fed finishing diet at three ages (A). Spring-born steers were started at 6 or 18 mo of age (A6 and A18), and fall-born steers were started at 12 mo of age (A12). Slaughter times (T) were at 0, 90, 180, and 270 d for A6; 68, 136, and 204 d for A12; and 0, 45, 90, and 135 d for A18. Data collected on each animal included feed intake, growth, chemical composition of the complete body and carcass, and quantitative and qualitative assessment of the meat produced. Four steers of each sire group were slaughtered in each of the 11 A-T treatment groups, and the experiment was repeated for 2 yr in the A12 groups and 3 yr in the A6 and A18 groups (n = 237). Steers sired by HG bulls were larger and produced larger carcasses and more carcass protein than MG-sired steers (S, P < .05 or .01). Steers sired by MG bulls were fatter, had higher quality grades, and accumulated fat at a faster rate than HG-sired steers, and this effect was greater in older steers (G and GA, P < .05 or .01). Sire growth potential did not affect gain, intake, live weight efficiency, tenderness, or taste panel scores (P > .2). Steers sired by HG bulls were more efficient at producing carcass weight and carcass protein at A12 and A18 than were MG-sired steers. At the end of the finishing period, older (A18), HG-sired steers were too large with insufficient fat by current industry standards, and younger (A6), MG-sired steers were too small. Our conclusions are that both HG- and MG-sired steers can produce acceptable carcasses for current market standards with comparable efficiencies of live-weight gain, but the growing and finishing strategy must be adapted to the genotype.     

Effects of Duroc, Meishan, Fengjing, and Minzhu boars on carcass traits of first-cross barrows.

Duroc, Meishan, Fengjing, and Minzhu boars were mated to crossbred gilts during two breeding seasons. From each sire breed group each season, six pens of approximately eight barrows each were slaughtered. A pen of pigs from each sire breed group was slaughtered at 7-d intervals from 168 to 203 d of age each season. Breed of sire effects were significant for all age-adjusted carcass traits except carcass length, fat thickness at the last rib, color score, and firmness score. At 184 d of age, Duroc crosses had the heaviest (P less than .05) slaughter and carcass weights; Minzhu crosses were lighter (P less than .05) than Meishan crosses but not lighter than Fengjing crosses. Differences among age-constant traits reflect differences in BW. After adjustment to a constant carcass weight of 78 kg, the three Chinese breeds had very similar carcass characteristics. Carcasses sired by Durocs had significantly less backfat and larger longissimus muscle area than carcasses sired by the Chinese breeds. Weight of each trimmed wholesale lean cut and their total weight were significantly higher for Duroc crosses than for Chinese crosses. Breed of sire means did not differ significantly for belly weight, but Duroc crosses had less (P less than .05) weight of leaf fat. Relative to Chinese crosses, longissimus muscles from Duroc crosses had more marbling (P less than .05). Sire breed groups did not differ significantly for color or firmness score. Pigs sired by Meishan, Fengjing, and Minzhu produced carcasses with significantly less lean content at a carcass weight of 78 kg than did pigs sired by Duroc.     

Effect of an accelerated finishing program on performance,carcass characteristics,and circulating insulin-like growth factor I concentration of early-weaned bulls and steers

Sixty-three Angus x Simmental calves were allotted to a bull or a steer group based on sire, birth date, and birth weight to determine effects of castration status on performance, carcass characteristics, and circulating insulin-like growth factor I (IGF-I) concentrations in early-weaned cattle. At 75 d of age, calves in the steer group were castrated. Calves were not creep-fed prior to weaning. All calves were weaned and weighed at an average age of 115 d and transported by truck to the OARDC feedlot in Wooster, OH. Performance and carcass characteristics were measured in three phases. Phase 1 was from 115 to 200 d of age, phase 2 was from 201 to 277 d of age, and phase 3 was from 278 d of age to slaughter. Before implantation, four bulls and four steers were selected for serial slaughter and carcass evaluation. Steers were implanted with Synovex-C at 130 d of age and with Revalor-S at 200 and 277 d of age. Serum samples were collected from all calves on the day of implantation, 28 and 42 d after implantation, and at slaughter and analyzed for circulating IGF-I concentration. Bulls gained 9.7% faster (1.75 vs 1.60 kg/d; P < 0.01), consumed 25 kg more DM (521 vs 496 kg; P = 0.11), and were 3.3% more efficient (282 vs 273 g/kg, P < 0.10) than steers in phase 1. However, steers gained 10.5% faster (1.62 vs 1.46 kg/d; P < 0.02), consumed similar amounts of DM, and were 6.5% more efficient than bulls (214 vs 201 g/kg; P < 0.06) in phase 2. Overall gains and efficiency were similar between bulls and steers; however, bulls consumed 140 kg more DM (P < 0.05), were 27 kg heavier (P < 0.05), and had to stay in the feedlot 18 more days (P < 0.05) than steers to achieve a similar amount of fat thickness. Implanted steers had greater concentrations of circulating IGF-I than bulls (P < 0.01), and the pattern of IGF-I concentration over time was affected by castration status (castration status x time interaction; P < 0.01). Synovex-C had a lower impact on circulating IGF-I concentration (implant effect, P < 0.01) than either Revalor-S implant. Eighty-five percent of both bulls and steers had marbling scores sufficient to grade low Choice or better. Bulls achieved their target fat thickness later, increased muscle growth, and deposited fat more favorably than steers, possibly due to a gradual increase in IGF-I concentration as the testicles grew rather than the large fluctuations in IGF-I concentration observed in steers following implantation.     

Growth, carcass composition and plasma melatonin in postpubertal beef heifers fed melatonin

Two experiments were conducted to determine if feeding melatonin alters plasma concentrations of melatonin, growth and carcass composition of postpubertal beef heifers exposed to 16 h light (L):8 h dark (D). In Exp. 1, 16 heifers were blocked by initial body weight (318 +/- 5.6 kg). Four heifers were killed before starting the melatonin treatment to obtain initial carcass composition. Six heifers received vehicle (95% ethanol) and six were fed melatonin (4 mg/100 kg body weight) daily for 58 d at 1330 to coincide with the middle of the 16-h light period. On d 59 heifers were slaughtered. Melatonin feeding increased the percentage of fat in rib (P less than .05) and longissimus muscle (LD; P less than .10) and carcass fat accretion 28% (P less than .09) but reduced the percentage of protein 8% in rib (P less than .05) and carcass protein accretion 30% (P less than .09). Other measures in the carcass and body weight gain were not affected (P greater than .10) by feeding melatonin. Plasma concentrations of melatonin increased (P less than .01) from 10 to 140 pg/ml within 30 min of feeding melatonin. In Exp. 2, 24 heifers were blocked by initial body weight (348 +/- 13.7 kg). Eight heifers were killed initially, eight received vehicle and eight were fed melatonin for 63 d as described in Exp. 1. Melatonin did not influence (P greater than .10) body weight gain or any measure in the carcass; however, these heifers were fatter (40.1%) than those in Exp. 1 (30.9%) at the beginning of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and carcass characteristics of cull cows after different times-on-feed

Cull cows (N = 48) of similar age from Angus and Hereford breed types were assigned to one of four feeding periods (0, 28, 56 or 84 d) and subdivided into two groups, one implanted with Synovex-H and a non-implanted control. Cows were fed a high energy diet and slaughtered at the end of each feeding period. Average daily gain and feed efficiency were evaluated on each animal during the trial. The following carcass traits were evaluated: USDA yield and quality grade characteristics, boning yield, muscle weights, bone weights, pH and Warner-Bratzler shear force of the longissimus muscle. The left side of each carcass was boned and proximate analysis was determined. No significant implant effects were encountered for any of the traits evaluated; therefore, data were pooled and evaluated by feeding period only. Carcass weight and boneless forequarter and hindquarter tissue weights increased significantly between each feeding period; percent kidney, pelvic and heart fat (KPH) and yield grade did not differ (P greater than .05) until d 56 and 84, respectively. Quality grade and marbling scores improved (P less than .05) between 28 and 56 d of feeding. Biceps femoris weight changed during the 84-d experiment from 4.1 kg on d 0 to 5.3 kg on d 84 (P less than .05). Proximate analysis of the boneless tissue indicated an increase (P less than .05) in extractable fat of approximately 6% for each feeding period (6.3% fat on d 0 to 25.4% on d 84).(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and carcass characteristics and serum growth hormone, prolactin and insulin profiles in Debouillet lambs treated with ovine growth hormone and(or) zeranol

Sixteen Debouillet wether lambs (approximately 3 mo old) were placed indoors in 1.5- x 3-m pens (14 h light:10 h dark) 28 d after weaning. Lambs received no implant or a 12-mg zeranol implant on d-2 (eight lambs/group). Two days later (d 0), animals received either 0 or 2.5 mg ovine growth hormone (oGH, eight lambs/group) s.c. on alternate days for 42 d. Animals had ad libitum access to water, salt, mineral and a pelleted alfalfa diet (16% CP). After 42 d, lambs were slaughtered to evaluate carcass traits, organ weights and femur characteristics. Zeranol by oGH interactions were not detected (P greater than .20). Zeranol increased (P less than .05) BW, improved (P less than .05) feed:gain during the first 20 d and increased (P less than .10) feed intake during the last 22 d of the 42-d trial compared with controls. Carcass characteristics were not altered (P greater than .10) by 12 mg zeranol. Serum insulin and prolactin were elevated (P less than .05), but serum GH was not influenced by zeranol compared with controls. Exogenous oGH decreased feed intake (P less than .10) and improved feed:gain (P less than .05) during the initial 20 d compared with controls, but did not influence (P greater than .20) these variables during the last 22 d of the study. Carcass traits were not influenced (P greater than .10) by oGH. Exogenous ovine GH dramatically elevated (P less than .05) serum GH, but did not affect serum insulin or prolactin (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Performance, body composition and carcass characteristics of finishing steers as influenced by previous forage systems

To evaluate effects of previous forage systems on feedlot performance, yearling Hereford steers (average initial weight of 249 kg) were grazed on tall fescue (TF), smooth bromegrass-red clover (BG-RC) or orchardgrass-red clover (OG-RC) pastures before finishing. Serial slaughter was utilized during the first 2 yr of this study to determine changes in carcass characteristics throughout finishing, while steers were slaughtered at approximately 29% body fat during the third year. Steers grazing TF entered the feedlot at lighter weights and maintained lighter weights throughout finishing (P less than .05) even though dry matter intakes and feed conversions were similar (P greater than .05) among treatments. Steers that previously grazed TF had less (P less than .05) body fat, body protein, fat thickness and marbling, smaller (P less than .05) ribeye areas and lower (P less than .05) USDA yield and quality grades than than those that grazed BG-RC and OG-RC. However, linear contrasts indicated that steers grazing TF were compensating in ribeye area, marbling and quality grade as days in feedlot increased. This was confirmed in the third-year study, since carcass characteristics were similar among all steers. During the third year, linear and quadratic contrasts indicated that steers that grazed TF partially compensated in body protein. As days in feedlot increased, live and hot carcass weights, body fat, fat thickness, kidney, pelvic and heart fat, marbling, and USDA yield and quality grades increased (P less than .05), while ribeye area and body protein plateaued. Although carcass characteristics were similar among treatments, steers backgrounded on TF entered the feedlot at lighter weights, and partially compensated in weight after 134 d of finishing.     

Growth, carcass traits, and fatty acid profiles of adipose tissues from steers fed whole cottonseed

To investigate the impact of dietary whole cottonseed (WCS) level on fatty acid composition, growth, and carcass traits, 45 Hereford steers were assigned to diets containing 0, 15, or 30% dietary WCS. The 15 and 30% WCS contributed an estimated 3.3 and 6.6% additional lipid, respectively, to the diets. After being fed for 54 d, all animals were weighed and slaughtered, and carcass measurements were obtained. There were no differences (P greater than .05) among dietary treatment groups in live weight or ADG for the 54-d feeding period. Control steers had larger (P less than .05) longissimus muscle areas than steers fed 30% WCS, which accounted for the advantage in yield grade (P less than .05) exhibited by the control group. Feeding of 30% WCS resulted in minor increases in linoleic and total polyunsaturated fatty acid content of perinephric fat expressed in both normalized (area percentage) and gravimetric (g/100 g of fresh tissue) formats. There were no significant differences in the monounsaturated or saturated fatty acid content of adipose tissues from animals fed the different diets. Subcutaneous adipose tissue samples were higher (P less than .01) in total unsaturates but had lower (P less than .05) proportions of C18:0 and C18:1 than perinephric samples. Feeding WCS at the levels reported herein only had minor effects on fatty acid composition of beef adipose tissues.     

Performance and carcass quality of steers supplemented with zinc oxide or zinc methionine

Forty-five Angus steers (avg initial wt 330 kg) were individually fed for 112 d to assess the value of supplemental Zn and source on performance and carcass quality. Steers had ad libitum access to a control diet (81 ppm Zn) of 33% whole corn, 33% ground milo, 15% cottonseed hulls and 13% cottonseed meal, or this control diet with 360 mg Zn/d added from either zinc methionine or zinc oxide. Steers were slaughtered on d 114, and carcass composition was determined by specific gravity. Average daily gain and feed efficiency were not affected by dietary treatments. Steers fed zinc methionine had a higher (P less than .05) USDA quality grade than those fed the control and zinc oxide diets. Marbling score was higher (P less than .05) for steers fed zinc methionine than for those fed control and zinc oxide treatments (4.4 vs 4.0 and 4.0, respectively, where 3 = slight, 4 = small, 5 = modest). Steers fed zinc methionine tended to have more (P less than .10) external fat (13 mm) than steers fed the control diet (10 mm); steers supplemented with zinc oxide had intermediate amounts of external fat (11 mm). Steers fed zinc methionine had 10.5 and 12.8% more (P less than .05) kidney, pelvic and heart (KPH) fat than steers fed control or zinc oxide diets, respectively. The effects of zinc methionine on carcass quality grade and marbling score may be due to Zn and (or) methionine. Regardless of the mechanism, the difference represents a potential economic benefit to producers.     

Influence of nutritional deprivation on insulin-like growth factor I, somatotropin, and metabolic hormones in swine

Although growth hormone (GH) is a primary stimulus for the synthesis of insulin-like growth factor I (IGF-I), other factors such as nutritional status, insulin, and thyroid hormones are important modulators of circulating IGF-I levels. Thus, the effects of feed restriction and subsequent refeeding on plasma levels of IGF-I, GH, insulin, and thyroid hormones were studied in swine. Despite an elevation in plasma GH levels after 48 h of feed restriction, circulating IGF-I levels were decreased by 53% (P less than .05). Plasma triiodothyronine (T3) and insulin were lower (P less than .05) within 24 h after the feed restriction began, whereas thyroxine (T4) did not decrease until 48 h after removal of feed. Blood glucose levels remained unchanged throughout the experiment. Refeeding after the 48-h fast was associated with a decline (P less than .05) in circulating GH levels within 2 h, concomitant with an elevation (P less than .05) in plasma insulin and T3. Refeeding fasted pigs was associated with an increase (P less than .05) in plasma IGF-I; however, levels still had not returned to prefast concentrations within 24 h after refeeding. These data indicate that the GH-IGF-I axis becomes uncoupled during nutritional restriction in swine and that inadequate nutrient supply may limit the expression of the anabolic effects of GH.