Effect of ractopamine hydrochloride on environmental gas emissions,growth performance,and carcass characteristics in feedlot steers

With a growing global population and increased environmental concerns around animal agriculture, it is essential to humanely maximize animal performance and reduce environmental emissions. This study aims to determine the efficacy of feeding ractopamine hydrochloride (RAC), an orally active, β ₁-adrenergic agonist (β₁AA), to feedlot steers in the last 42 d of finishing to reduce ammonia (NH₃) emissions and improve animal performance. A randomized complete block design was used to allocate 112 Angus and crossbred Angus steers (initial body weight [BW] = 566.0 ± 10.4 kg) to 8 cattle pen enclosures. Pens (n = 4 per treatment, 14 steers per pen, and 56 steers per treatment) were randomly assigned to one of two treatments: 1) CON; finishing ration containing no RAC, 2) RAC; finishing ration containing 27.3 g/907 kg dry matter (DM) basis RAC. Steers were weighed on day −1 and 0 before treatment and day 14, 28, and 42 during treatment. Treatment rations were mixed and delivered daily by masked personnel. Measured emissions included NH₃, nitrous oxide (N₂O), methane (CH₄), hydrogen sulfide (H₂S), and carbon dioxide (CO₂). The primary response variables assessed were emissions standardized by live weight (LW) and hot carcass weight (HCW). Steers were harvested on day 43 and carcass data were collected on day 43 and 44. Steers fed RAC reduced NH₃ emissions by 17.21% from day 0 to 28 (P = 0.032) and tended to reduce NH₃ from day 0 to 42 by 11.07% (P = 0.070) vs. CON. When standardized for LW, NH₃ was reduced by 23.88% from day 0 to 14 (P = 0.018), 17.80% from day 0 to 28 (P = 0.006), and 12.50% for day 0 to 42 (P = 0.027) in steers fed RAC vs. CON. Steers fed RAC had 14.05% (P = 0.013) lower cumulative NH₃ emissions when standardized by HCW vs. CON. Feeding RAC to Steers reduced H₂S by 29.49% from day 0 to 14 (P = 0.009) and tended to reduce H₂S over day 0 to 28 by 11.14% (P = 0.086) vs. CON. When H₂S emissions were standardized for LW, RAC fed steers had a 28.81% reduction from day 0 to 14 (P = 0.008) vs. CON. From day 0 to 42 the RAC fed steers tended to have a 0.24 kg/d greater average daily gain (ADG) (P = 0.066) and tended to eat 4.27% less (P = 0.069) on a DM basis vs. CON. The RAC fed steers had a 19.95% greater gain to feed ratio (G:F) compared to CON (P = 0.012). Steers fed RAC had an average of 12.52 kg greater HCW (P = 0.006) and an increase of 1.93 percentage units in dressing percent (DP) (P = 0.004) vs. CON. Ractopamine is an effective medicated feed additive for reducing NH₃ and improving end product performance through HCW yields.     

Effects of ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers

An experiment was conducted to determine the relationship between feeding ractopamine and different amounts of MP on growth and carcass characteristics of feedlot heifers. Seventy-two crossbred heifers (475 kg of initial BW) were fed individually a diet based on steam-flaked corn for ad libitum intake for 29 d. Heifers were implanted with 140 mg of trenbolone acetate and 14 mg of estradiol-17beta 60 d before the experiment. Treatments were arranged as a 2 x 3 factorial and included 0 or 200 mg of ractopamine-HCl (23 ppm)/ d, and urea, solvent soybean meal, or expeller soybean meal (ESBM) as the predominant protein supplement. The amounts of MP supplied by the urea, solvent soybean meal, and ESBM diets were 688, 761, and 808 g/ d, respectively, calculated according to level 1 of the NRC model. Body weights were obtained 1 d before ractopamine feeding and at slaughter. Blood samples were obtained 1 d before starting the experiment and 13 d later. Ractopamine improved ADG, efficiency of gain, carcass-adjusted ADG, and carcass-adjusted efficiency of gain (P < 0.01). For ADG, heifers demonstrated a ractopamine x protein source interaction (P < 0.05); heifers not fed ractopamine had greater ADG when fed ESBM than when fed urea, whereas for heifers fed ractopamine there were no differences (P > or = 0.10) among protein supplements. This interaction was not observed for carcass-adjusted ADG (P = 0.60). Final live weights (P = 0.02) and carcass weights (P = 0.01) were greater with ractopamine feeding. Carcass marbling scores and yield grades were not affected by ractopamine or protein source (P > or = 0.39). Plasma total alpha-amino N and glucose concentrations decreased more from pretreatment concentrations when heifers were fed ractopamine (P < 0.05). Feeding ractopamine to heifers for 28 d before slaughter improved ADG and efficiency of gain without any large effects on carcass characteristics. The MP supply does not need to be increased from that provided by finishing diets based on steam-flaked corn with urea as the primary N supplement to allow the maximal response to ractopamine by finishing heifers.     

Effects of ractopamine supplementation and postmortem aging on longissimus muscle palatability of beef steers differing in biological type

Effects of ractopamine hydrochloride (RAC) supplementation and postmortem aging on palatability of beef from steers differing in biological type were evaluated using LM samples from British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 98/type). Equal numbers of steers within each type were assigned to treatments of 0 or 200 mg.steer(-1).d(-1) of RAC fed during the final 28 d of the finishing period. Warner-Bratzler shear force (WBSF) was measured at 3, 7, 14, and 21 d postmortem, and trained sensory panel (TP) evaluation was conducted using LM samples aged for 14 d postmortem. A RAC x type interaction (P = 0.006) was detected for WBSF. Within each type, steers fed RAC produced steaks with greater (P < 0.05) WBSF values than steaks from control steers; however, the magnitude of the effect of RAC on WBSF was more pronounced among Brahman cross-breds (5.53 vs. 4.96 +/- 0.10 kg) than among Continental crossbred (4.16 vs. 3.96 +/- 0.10 kg) and British steers (4.10 vs. 3.75 +/- 0.10 kg). The effect of RAC on WBSF, though diminished slightly by aging (mean WBSF difference: 3 d = 0.49 kg; 21 d = 0.24 kg), was not completely mitigated by 21 d of postmortem storage (P(RAC x AGE) = 0.16). Steers fed RAC produced steaks that received lower (P < 0.05) TP ratings for tenderness (8.09 vs. 8.95 +/- 0.18) and juiciness (7.41 vs. 8.07 +/- 0.16 kg), along with slightly lower (P = 0.06) ratings for beef flavor (6.67 vs. 6.93 +/- 0.10 kg), compared with steaks from unsupplemented steers, regardless of biological type. Among the 3 biological types, Brahman crossbred cattle produced steaks with the greatest (P < 0.05) WBSF values at each aging period; WBSF values for steaks from British and Continental type steers did not differ (P > 0.05) at any aging time. Sensory panel ratings of tenderness, juiciness, and beef flavor were greatest (P < 0.05) for steaks from British steers, and least (P < 0.05) for steaks produced by Brahman-type steers. Results from this study suggest that RAC supplementation slightly decreases LM tenderness (WBSF and TP) of British, Continental crossbred, and Brahman cross-bred steers, and that the effect of RAC on WBSF may be more pronounced in steaks from Brahman crossbred cattle than among stenks from Continental type or British steers.     

Effects of programmed growth rate and days fed on performance and carcass characteristics of feedlot steers.

Two experiments were conducted to investigate a feeding regimen in which a programmed amount of feed was offered daily to control growth rate of steers. In Exp. 1, steers (n = 107, 309 +/- 3 kg) were used to determine effects of offering ad libitum access to feed (AL) vs a programmed intake feeding regimen (PI) and the number of days steers were fed (168 vs 203) on performance and carcass characteristics. Steers in the programmed intake feeding regimen were fed to achieve a predicted gain of 1.13 kg/d for the first 78 kg of gain, 1.36 kg/d for the next 124 kg of gain, and were given ad libitum access to feed for the final 54 or 103 kg of gain before slaughter (for steers fed for 168 d or 203 d, respectively). Feed efficiency was greater (P < 0.02) for steers in the PI than for those in the AL feeding regimen (0.193 vs 0.183 kg gain/kg feed, respectively). From d 169 to 203, steers in the PI feeding regimen had greater (P < 0.06) ADG (1.60 vs 1.38 kg/d) and similar (P = 0.38) feed efficiency than steers in the AL regimen. In Exp. 2, steers (n = 96; 308 +/- 3 kg BW) were offered feed ad libitum throughout the experiment (AL) or were programmed to gain at a high (PI-H) or low (PI-L) growth rate. For the first 78 kg of gain, intake was restricted to achieve predicted gains of 1.13 kg/d (PI-L) or 1.25 kg/d (PI-H). For the next 124 kg of gain, intake was restricted to achieve predicted gains of 1.36 kg/d (PI-L) or 1.47 kg/d (PI-H). Feed was offered ad libitum for the final 58 kg of gain. Overall ADG was similar (P > 0.37) among feeding regimens despite lower DMI for the steers in the PI-L and PI-H feeding regimens than for those in the AL regimen. Feeding regimen did not affect (P < 0.22) carcass characteristics. Programmed intake feeding regimens sustained growth rate and feed efficiency for an extended period of time without detrimental effects on carcass characteristics.     

Effects of sequential implanting and ractopamine hydrochloride supplementation on carcass characteristics and longissimus muscle tenderness of calf-fed steers and heifers

A 4 × 2 factorial arrangement of treatments (4 growth-enhancement treatments × 2 sex classes) was used to quantify effects of initial implanting (I-implant, d 0), terminal implanting (T-implant, d 63), and feeding ractopamine hydrochloride [RAC, 200 mg/(animal/d)] for the last 28 d on feed on carcass characteristics and LM shear force (WBSF) of calf-fed steers (n = 159) and heifers (n = 132). Growth-enhancement treatments included the following: TRT1, T-implant only; TRT2, I-implant and RAC; TRT3, I-implant and T-implant; TRT4, I-implant, T-implant, and RAC. Growth responses (BW and ADG) were measured in 3 segments of the finishing period: 1) d 0 to 63, 2) d 63 to 28 d before slaughter, and 3) final 28 d. Cattle were slaughtered after 152, 166, or 180 d of finishing; carcass data were collected after a 48-h chill; and LM WBSF was measured at 3, 7, 14, 21, and 28 d postmortem. A priori contrasts were constructed to test effects associated with use vs. exclusion of growth enhancement in each segment of the finishing period. The interaction between sex class and treatment was not significant (P > 0.05) for any trait tested, indicating that the 4 treatments elicited similar effects in both sexes. Initial implanting improved (P < 0.001) ADG from d 0 to 63 by 11.5%, terminal implanting improved (P < 0.001) ADG from d 63 to 28 d before slaughter by 15%, and supplementing twice-implanted cattle with RAC enhanced ADG during the final 28 d of finishing by 12%. Effects of I-implant, T-implant, and RAC resulted in LM area increases of 3 cm(2) (P = 0.015), 6 cm(2) (P < 0.001), and 3 cm(2) (P = 0.011), respectively, and HCW responses of 11 kg (P = 0.011), 16 kg (P = 0.001), and 6 kg (P = 0.195), respectively. Initial implanting resulted in a 20-point reduction (P = 0.097) in marbling, and T-implant reduced marbling by 25 points (P = 0.04), whereas marbling score was unaffected (P = 0.236) by RAC supplementation. Cattle that received only 1 implant (TRT1 and TRT2) produced carcasses with greater (P = 0.026) mean marbling scores and greater (P = 0.01) rates of conformity to beef carcass marketing specifications for HCW, quality grade, yield grade, and LM area than did cattle that were implanted twice (TRT3 and TRT4). Values for LM WBSF were not affected (P > 0.05) by initial or terminal implanting; however, RAC supplementation increased (P = 0.007) mean LM WBSF by 0.23 kg, which translated into a reduction (P = 0.007) in predicted consumer acceptance of LM steaks.     

Effect of age at feedlot entry on performance and carcass characteristics of bulls and steers

Seventy Angus x Simmental calves (BW = 166.3 +/- 4.2 kg) were used in a 3 x 2 factorial arrangement to determine the effect of age at feedlot entry and castration on growth, performance, and carcass characteristics. At 82 d of age, steers were castrated. Calves were placed in the feedlot at 111 (early-weaned), 202, or 371 (yearling) d of age. Steers were implanted with Synovex-S followed 93 d later with Revalor-S. Calves were harvested on an individual basis when fat thickness was estimated to be 1.27 cm. During the feedlot phase, yearlings gained faster (P < 0.01) than calves placed in the feedlot at 202 or 111 d of age (1.88, 1.68, and 1.62 kg/d, respectively); however, from 111 d of age until harvest, ADG was greatest for early-weaned calves, intermediate for cattle placed in the feedlot at 202 d of age, and lowest for yearlings (1.62, 1.47, and 1.21 kg/d, respectively; P < 0.01). Early-weaned calves spent the most days in the feedlot, followed by calves placed in the feedlot at 202 d of age; yearlings spent the fewest days in the feedlot (221, 190, and 163 d, respectively; P < 0.01). Total DMI when in the feedlot was similar (P = 0.22) among age groups; however, daily DMI was lowest for early-weaned calves, intermediate for calves placed in the feedlot at 202 d of age, and the highest for yearlings (7.1, 8.1, 10.5 kg/ d, respectively; P < 0.01). Early-weaned calves were the most efficient, followed by calves placed in the feedlot at 202 d of age; yearlings were the least efficient (227, 207, 180 g gain/kg feed, respectively; P < 0.01). Weight at harvest (682, 582, 517 kg, respectively; P < 0.01) and hot carcass weight (413, 358, 314 kg, respectively; P < 0.01) were greatest for yearlings, intermediate for cattle placed in the feedlot at 202 d of age, and lowest for early-weaned calves. Early-weaned calves had the smallest longissimus area, followed by calves placed in the feed-lot at 202 d of age; yearlings had the largest longissimus area (77, 86, 88 cm2, respectively; P < 0.01). Calves placed in the feedlot at 111 and 202 d of age had lower yield grades (3.2, 3.1, 3.5, respectively; P < 0.04), and produced fewer select carcasses than yearlings (25, 13, 48%, respectively; P < 0.01). Bulls and implanted steers both had an ADG of 1.7 kg/d when in the feedlot; however, bulls had a greater (P < 0.09) hot carcass weight (370 vs 354 kg) and a larger (P < 0.01) longissimus area (85.8 vs 81.3 cm2) than steers. Earlier feedlot placement resulted in greater quality grades but lower carcass weights.     

Effects of water sulfate concentration on performance, water intake, and carcass characteristics of feedlot steers.

Two hundred forty single-source, cross-bred steers (304 kg) were used to evaluate the effects of various water sulfate concentrations on performance, water intake, and carcass characteristics of feedlot steers. Cattle were stratified by weight and assigned within weight blocks to five water treatments. Averaged over time, actual water sulfate concentrations (+/- SEM) were 136.1 (+/- 6.3), 291.2 (+/- 15.3), 582.6 (+/- 16.9), 1,219.2 (+/- 23.7), and 2,360.4 (+/- 68.2) mg/L, respectively. Weather-related data were recorded. Increasing water sulfate concentration resulted in linear decreases in ADG (P < 0.01) and gain:feed ratio (P < 0.01) and a quadratic effect on water intake (P = 0.02) and tended to quadratically increase then decrease DMI (P = 0.13). Sulfate x period interactions were evident for DMI (P = 0.01), ADG (P < 0.01), and feed efficiency (P < 0.01). Time had quadratic effects on DMI, water intake, ADG, and feed efficiency (P < 0.01 for all models). Increasing water sulfate concentration resulted in linear decreases in final weight, hot carcass weight, and dressing percentage, a linear increase in longissimus muscle area, and a quadratic effect on fat thickness over the 12th rib and predicted yield grade (P < 0.05 for all dependent variables). Mean daily temperature explained 25.7% of the observed variation in water intake. Other factors that explained a significant (P < 0.01) amount of variation in water intake were BW, DMI, water sulfate concentration, barometric pressure, wind speed, and humidity. High water sulfate concentrations had a significant and deleterious effect on performance and carcass characteristics of feedlot steers. Increasing the sulfate concentration in water may have resulted in a functional water restriction early in the trial when ambient temperatures were greatest. However, toward the latter stages of the trial, cattle supplied higher-sulfate water had higher ADG and FE. These improvements later in the trial may represent compensatory gain associated with decreased ambient temperature and water requirements. Averaged over time, a water sulfate concentration of greater than 583 mg/L, equivalent to 0.22% of the diet, decreased feedlot performance.     

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.     

A dose-response study of melengestrol acetate on feedlot performance and carcass characteristics of beef steers

The dose response of melengestrol acetate (MGA) on ADG (kg/d) and gain efficiency (gain/DMI, g/kg) was estimated in beef steers fed a finishing diet under commercial feedlot conditions. Melengestrol acetate is not approved for use in steers as a feed additive. The study design was five blocks of four pens (each pen was assigned a dose of MGA) with 166 to 200 steers per pen. Melengestrol acetate was fed to steers at 0 (n = 899, five pens), 0.1 (n = 900, five pens), 0.2 (n = 899, five pens), and 0.4 (n = 900, five pens) mg of MGA/steer daily. Pens within a block were slaughtered on the same day. Blocks 1 through 5 were fed MGA for 123, 122, 116, 124, and 138 d, respectively. The experimental unit was a pen of steers, and blocking was based on source of steers. The ADG was 1.81, 1.85, 1.80, and 1.83 kg/d for steers fed 0, 0.1, 0.2, and 0.4 mg MGA per day, respectively. For ADG, the dose was significant, but neither linear nor quadratic effects were significant. Compared with steers of the control group, ADG was greater for steers fed 0.1 mg MGA (P < 0.01). Feed efficiencies were 170, 173, 171, and 172 g/kg for steers fed 0, 0.1, 0.2, and 0.4 mg MGA/d, respectively; however, no effects of dose (P = 0.19) or linear (P = 0.21) or quadratic (P > 0.60) effects were observed. There was no evidence for either positive or negative effects of MGA on DMI, hot carcass weight, dressing percent, quality grade, yield grade, back fat thickness, marbling score, longissimus muscle area, and incidence of dark cutter carcasses in response to feeding MGA to steers at doses of 0.1, 0.2, and 0.4 mg daily. The incidence of buller behavior (0.43 to 1.11%) was low and did not permit an accurate test of the clinical observations that feeding MGA to steers decreases the occurrence of buller steers. Melengestrol acetate fed to finishing beef steers produced small improvements in growth performance (ADG, 2.2%) at the 0.1 mg MGA dose, but none of the doses examined produced improvement in carcass quality or yield grade measurements.     

Meta-analysis of factors affecting carcass characteristics of feedlot steers

A meta-analysis was conducted to assess the effects of biological type (early-moderate or late maturity) and implant status (estrogenic, combination, or nonimplanted; repeats included) on HCW (kg); LM area (cm2); 12th-rib fat thickness (fat thickness, cm); KPH (%), and intramuscular fat (%) at harvest, to provide inputs to an ongoing program for modeling beef cattle growth and carcass quality. Forty-three publications from 1982 to 2004 with consistent intramuscular fat data were evaluated. Two studies were undertaken: 1) with fat thickness as a covariate and 2) with BW as a covariate. The intercept-slope covariance estimate was not statistically different from 0 for LM area (P = 0.11), KPH (P = 0.19), and intramuscular fat (P = 0.74) in study 1, and for LM area (P = 0.44), fat thickness (P = 0.11), KPH (P = 0.19), and intramuscular fat (P = 0.74) in study 2; therefore, a reduced model without a covariance component was fitted for these carcass characteristics. A covariance component was fitted for HCW (P = 0.01, study 1 and P = 0.05, study 2) and for intramuscular fat (P = 0.05, study 2). In study 1, the results for maturity indicated differences between early-moderate and late maturity for HCW (P < 0.01) and LM area (P < 0.01) but no differences for KPH (P = 0.26) and intramuscular fat (P = 0.50); for implant status, an estrogenic or combination implant increased HCW by 2.9% (P = 0.27) or 4.8% (P < 0.01), increased LM area by 3.2% (P = 0.23) or 6.3% (P < 0.01), decreased intramuscular fat by 8.1% (P < 0.01) or 5.4% (P < 0.01), respectively, and decreased KPH by 7.6% (P = 0.34) for estrogenic implants but increased KPH by 1.1% (P = 0.36) for combination implants, compared with nonimplanted steers. In study 2, the results at 600 kg of BW for implant status (implant or nonimplant) indicated no differences for HCW (P = 0.63) and LM area (P = 0.73), but there were differences for fat thickness (P < 0.01), KPH (P < 0.01), and intramuscular fat (P < 0.01); the results for maturity (early-moderate or late maturity) indicated no differences for HCW (P = 0.94), but there were differences for LM area (P < 0.01), fat thickness (P < 0.01), KPH (P < 0.01), and intramuscular fat (P < 0.01). The difference between early-moderate and late maturity (studies 1 and 2) confirmed that frame size accounts for a substantial portion of the variation in carcass composition. Studies 1 and 2 also indicate that implant status had significant effects on carcass quality.     

Effects of calcium soaps of long-chain fatty acids on feedlot performance, carcass characteristics and ruminal metabolism of steers

Two trials were conducted to determine the effects of calcium soaps of long-chain fatty acids (calcium soap) on feedlot performance, diet digestibility, carcass characteristics and ruminal metabolism of steers fed diets (85% concentrate:15% corn silage) containing 0, 2, 4 or 6% calcium soap. In Trial 1, increasing calcium soap decreased (P less than .05) DM, CP and gross energy intake but increased total fatty acid intake. Feed to gain ratio tended to improve with increased calcium soap; gross energy conversion was not affected (P greater than .05) by diet. Average daily gain and hot carcass weight decreased (P less than .05) with addition of calcium soap; other carcass characteristics were not affected (P greater than .05). Apparent digestibilities of DM, N, energy and ash were not affected (P greater than .05) by calcium soap. Neutral detergent fiber digestibility increased linearly (P less than .08) with increasing calcium soap, whereas digestibility of total fatty acids was affected quadratically (P less than .05); fatty acid digestibility was similar among 0, 2 and 4% calcium soap diets but decreased for the 6% calcium soap diet. In Trial 2, increased calcium soap did not affect (P greater than .05) ruminal VFA concentrations, pH or in sacco NDF disappearance of orchardgrass following 12, 24 and 48 h of incubation. Calcium soap increased (P less than .07) ruminal concentrations of calcium soap fatty acids at 1, 2, 4 and 8 h postfeeding. Calcium soap did not improve performance of feedlot cattle fed high-concentrate diets. Further, calcium soap did not affect ruminal fermentation and did not dissociate significantly even when ruminal pH was below 6 for extended periods of time.     

Effects of feeding polyclonal antibody preparations on rumen fermentation patterns, performance, and carcass characteristics of feedlot steers

In a previous study, preparations of polyclonal antibodies (PAP) against Fusobacterium necrophorum (PAP-Fn) or Streptococcus bovis (PAP-Sb) were successful in decreasing ruminal counts of target bacteria and increasing ruminal pH in steers fed high-grain diets. The objective of this study was to evaluate the effects of feeding PAP-Fn or PAP-Sb on performance, carcass characteristics, and ruminal fermentation variables of feedlot steers. In Exp. 1, during 2 consecutive years, 226 or 192 Angus and Angus crossbred steers were fed a high-grain diet containing either PAP-Sb or PAP-Fn, or both. When measured on a BW basis, steers fed only PAP-Sb had a greater G:F (P < 0.05) than those fed no PAP. Nevertheless, when both PAP were fed, feed efficiency was similar (P > 0.10) to steers fed no PAP or only PAP-Sb. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a decreased (P < 0.05) dressing percentage. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a decreased severity of liver abscess (P < 0.05). No differences (P > 0.10) were observed in any other carcass characteristics. In Exp. 2, sixteen ruminally cannulated Angus crossbred steers (BW = 665 +/- 86 kg) were fed a high-grain diet containing either PAP-Sb or PAP-Fn, or both. Feeding only PAP-Fn or PAP-Sb for 19 d decreased (P < 0.05) ruminal counts of S. bovis when compared with steers fed both or no PAP. The ruminal counts of F. necrophorum in steers fed PAP-Fn alone or in combination with PAP-Sb were decreased by 98% (P < 0.05) after 19 d, when compared with the counts in control steers. Mean daily ruminal pH was greater (P < 0.05) in steers fed both PAP when compared with feeding either or no PAP. Ruminal pH in the first 4 h after feeding was greater (P < 0.05) for steers receiving PAP-Fn alone or in combination with PAP-Sb. Steers receiving either PAP alone or in combination had less (P < 0.05) ruminal NH(3)-N concentrations in the first 4 h after feeding when compared with those of control steers. Polyclonal antibody preparations against S. bovis were effective in enhancing G:F of steers fed high-grain diets, but dressing percentage was decreased. Mechanisms of enhancement of G:F remain unknown but may be related to changes in ruminal counts of target bacteria and associated effects on ruminal fermentation products.     

Effects of vitamin A on growth performance and carcass quality in steers

Vitamin A plays a critical role in many essential life processes. In herbivores, it is either derived from plant β-carotene or directly as a dietary supplement. In cattle, vitamin A has the potential to influence various carcass traits that are sought by specific beef markets. A group of 20 Angus steers was removed from pasture and fed a low β-carotene and vitamin A cereal-based ration on a feedlot for 308 days. Ten of the steers were supplemented with vitamin A (retinyl palmitate, 60 IU of vitamin A/100 kg body weight/day) and the other ten received no supplement. The results demonstrated that restriction of vitamin A intake changed intramuscular fat deposition without changing subcutaneous fat depots. Angus steers that had been depleted of vitamin A showed increased intramuscular fat in the longissimus thoracis et lumborum (LTL) by 35% (P < 0.026) and seam fat area at the quartering site by 33% (P < 0.0273), when compared with cattle supplemented with vitamin A. There were no changes in intramuscular fat in the semitendinosus. Visually assessed marbling scores were also higher (19%; P < 0.094) in the non-supplemented, depleted group. There was no effect of vitamin A depletion on cattle growth and other meat traits (eye muscle area, meat colour, pH, meat cut weight), meat eating attributes (tenderness, cooking loss) or muscle fibre diameter. The only difference (P < 0.0177) among the meat traits was fat colour where depleted animals had whiter fat than the controls. Moreover, the fat from the vitamin A depleted group was softer with a lower melting point. We conclude that the reduced vitamin A consumption, leading to vitamin A depletion, increases intramuscular fat. On the other hand, the vitamin A depletion did not increase subcutaneous fat depth or change other meat quality traits, suggesting that marbling and these other traits are not invariably related.     

Effects of dietary zilpaterol hydrochloride on feedlot performance and carcass characteristics of beef steers fed with and without monensin and tylosin

A feedlot experiment was conducted under commercial conditions in the Texas Panhandle using 3,757 feedlot steers (average of 94 steers/pen) to evaluate the effects of feeding zilpaterol hydrochloride with or without monensin and tylosin on feedlot performance and carcass characteristics. The experiment was conducted using a randomized complete block design. Treatments were arranged as a 2 (no zilpaterol vs. zilpaterol) x 2 (monensin and tylosin withdrawn vs. monensin and tylosin fed during the final 35 d on feed) factorial. Steers were fed for a total of 161 to 167 d, and treatments were administered during the final 35 d that cattle were on feed. When included in the diet, zilpaterol, monensin, and tylosin were supplemented at 8.3, 33.1, and 12.2 mg/kg (DM basis), respectively. Zilpaterol was included in the diet for 30 d at the end of the finishing period and withdrawn from the diet for the last 5 or 6 d cattle were on feed. Cattle were harvested and carcass data collected. There were no zilpaterol x monensin/tylosin interactions (P >or= 0.12) for ADG or G:F. Feeding zilpaterol increased ADG (P < 0.001) by 0.20 kg and G:F (P < 0.001) by 0.029 kg/kg during the last 35 d on feed. Likewise, when feedlot variables were measured throughout the entire 161- to 167-d feeding trial, ADG (3.4%; P < 0.001) and G:F (3.9%; P < 0.001) were increased. Feeding zilpaterol increased (P < 0.001) dressing percent and HCW and decreased (P < 0.001) total liver abscess rate compared with controls. In addition, zilpaterol increased (P < 0.001) LM area by an average of 8.0 cm(2). There was a zilpaterol x monensin/tylosin interaction (P = 0.03) for marbling score. Zilpaterol decreased (P < 0.001) marbling score regardless of monensin and tylosin treatment, although withdrawal of monensin and tylosin for 35 d decreased marbling to a greater extent (31 vs. 17 degrees). Zilpaterol decreased (i.e., improved; P < 0.001) calculated yield grade regardless of monensin and tylosin treatment, but feeding zilpaterol in combination with the withdrawal of monensin and tylosin for 35 d decreased calculated yield grade to a greater extent (0.49 vs. 0.29) compared with the zilpaterol, monensin, and tylosin combination treatment (zilpaterol x monensin/tylosin interaction, P = 0.03). Results suggest that monensin and tylosin can be withdrawn from the diet during the zilpaterol feeding period (final 35 d on feed) with minimal effect on animal performance, although feeding zilpaterol in combination with monensin and tylosin seemed to moderate effects on carcass quality.     

Effects of weaning age and diet on growth and carcass characteristics in steers

Two experiments were conducted to determine the effects of diet on growth of steers weaned at approximately 100 vs 205 d of age. In Exp. 1, a 2 x 2 x 2 factorial experiment was conducted using 78 Angus crossbred cow-calf pairs. The factors examined were age at weaning (early, at 103+/-3 d [EW] vs normal, at 203+/-3 d [NW]), feeding strategy (ad libitum vs postweaning programmed intake), and dietary CP concentration (100 vs 120% of NRC [1984] recommended levels). Early-weaned calves had a greater (P < .001) ADG than NW calves from 103 to 203 d and reached market weight at 385 d vs 418 d for NW calves (P < .001). Likewise, steers offered feed for ad libitum consumption reached market weight at 394 d, compared with 409 d for programmed-intake steers (P < .05). In Exp. 2, 64 Angus crossbred steers were either weaned at 93+/-3 d and fed one of four diets, weaned at 210+/-3 d without access to creep feed, or weaned at 210+/-3 d with access to creep feed for 60 d prior to weaning. Early-weaned calves were heavier (P < .01) than NW calves at 210 d if fed either 100 or 90% concentrate diets, and they had greater (P < .001) backfat thickness at 210 d but no difference (P > .10) in longissimus muscle area compared to EW calves fed a 60% concentrate diet. At slaughter, 80 to 100% of steers on all treatments graded low Choice or higher. Feeding high-concentrate diets to EW beef calves accelerated growth rate and fat deposition early in the feeding period and may be a way to provide young cattle for a high-quality beef market.     

Effect of ractopamine hydrochloride and zilpaterol hydrochloride on growth,diet digestibility,intake and carcass characteristics of feedlot lambs

The effects of the β-adrenergic agonists ractopamine hydrochloride (RH; 0.35, 0.70 and 1.05 mg kg^− 1 of BW d^− 1) and zilpaterol hydrochloride (ZH; 0.10, 0.20 and 0.30 mg kg^− 1 of BW d^− 1) on growth performance and carcass characteristics were determined in 84 Dorper × Katahdin lambs (12 lambs per treatment), that were randomly assigned to a complete block design during a 42-day feeding trial. Lambs were fed a corn grain-based diet (18.71% CP and 12.9 MJ/kg ME). Nutrient digestibility of diets and blood serum metabolites were also determined. There were no significant (P > 0.05) differences in growth characteristics by effect of ZH or RH administration. However, lambs final weight, total weight gain and ADG increased linearly (P < 0.05) as levels of both β-adrenergic agonist increased. RH or ZH administration did not affect feed efficiency, diet digestibility or particular blood serum metabolites of lambs. Carcass characteristics of lambs consuming ZH were significantly better (P < 0.01) than RH or control lambs; RH produced significant linear response on carcass weight, dressing percentage, longissimus muscle area, carcass conformation and quality grade, and improved quadratically (P < 0.05) fat thickness and USDA yield grade of lamb carcasses. On the other hand, increasing levels of ZH decreased linearly (P > 0.01) fat thickness and improved (P > 0.05) USDA yield grade and carcass quality grade. Both β-adrenergic agonists improved carcass characteristics; although greater improvements were obtained with ZH than RH for most carcass characteristics.     

Effect of prenatal androgenization on growth performance and carcass characteristics of steers and heifers

Two experiments were conducted in which pregnant crossbred cows were randomly assigned to a control group or implanted with testosterone propionate/silastic implants between d 110 and 140 of gestation in Exp. 1 and between d 80 and 110 of gestation in Exp. 2. Androgenized heifers (TH) and treated steers (TS), born to implanted dams, possessed similar birth weights compared with control heifers (CH) and steers (CS), respectively, in both experiments. In Exp. 1, yield grades were lower (P less than .05) for TH than for CH. In Exp. 2, TH possessed 9.4% greater (P less than .07) 205-d adjusted weaning weights and 9.8% heavier (P less than .05) adjusted yearling weights than CH. In Exp. 2, daily gain was 19.5% faster (P less than .05) and feed intake was 13.6% greater (P less than .05) for TH than for CH. In Exp. 2, TH possessed less (P less than .05) s.c. fat, greater (P less than .10) carcass weight gains and lower (P less than .05) yield grades than CH. Liver weight per unit of carcass weight was greater (P less than .07) for TH than for CH in Exp. 2. Androgenized heifers had lower (P less than .07) lipid content in the 9-10-11th rib section than did CH. Calving intervals were similar for implanted and nonimplanted cows in both experiments. Results from these two trials suggest that efficiency of heifers for producing carcass beef can be improved by prenatal testosterone exposure.     

Biological type effects on postweaning growth, feed efficiency and carcass characteristics of steers

Postweaning growth, feed consumption and carcass characteristics of 259 individually fed F1 Angus-, Red Poll-, Pinzgauer-, Simmental- and Tarentaise-sired steers from Hereford dams were compared. Average daily gain to 382 d of age for Simmental-sired steers exceeded (P less than .05) the ADG for Red Poll, Angus and Pinzgauer, which were not different. Tarentaise-sired steers were intermediate in growth rate. Simmental-sired steers required less (P less than .05) feed per kilogram of gain than Red Poll- and Angus-sired steers to reach either 382 d of age or 400 kg. Feed conversion (FC) by Simmental, Pinzgauer and Tarentaise-sired steers did not differ (P greater than .05), nor did FC by Red Poll- and Angus-sired steers to reach 382 d or 400 kg. Angus-sired steers required less ME per kilogram of gain to reach 12.7 mm of carcass backfat than did Red Poll-, Pinzgauer- or Tarentaise-sired steers, which were similar. Simmental-sired steers were intermediate in feed conversion to 12.7-mm fat depth and did not differ from the other breed groups. Rankings of breed groups for traits indicative of lean tissue growth were similar to rankings for live animal growth traits. At age- and weight-constant endpoints, Angus-sired steers had more (P less than .05) fat cover and marbling than did steers sired by the other breeds. At these endpoints, Red Poll-sired steers also had more (P less than .05) fat cover than did Pinzgauer-, Simmental- and Tarentaise-sired steers, which were similar.     

Effects of forage and protein source on feedlot performance and carcass traits of Holstein and crossbred beef steers.

Fifty-eight Holstein and 58 crossbred beef steers were individually fed one of four isonitrogenous diets to evaluate the effects of forage source (corn silage and alfalfa haylage) and protein source (soybean meal and fish meal) on feedlot performance. Phase 1 diets (up to 354 kg of BW) were 40% forage and 60% concentrates and were fed for 70 to 136 d (depending on diet and breed group). Phase 2 diets (354 kg of BW until slaughter) were 20% forage and 80% concentrates and were fed for 127 to 150 d (depending on diet and breed group). Slaughter end points were .6 cm of 12th rib fat for Holsteins and 1.0 cm of rib fat for crossbreds using real-time ultrasonic estimates. The steers were fed for a maximum of 330 d each year. Forage source was a significant component of variation for most growth, efficiency, and carcass traits. Holstein and crossbred steers fed alfalfa haylage had significantly lower average daily gain, feed efficiency, dressing percentage, and empty body fat and required more days on feed to reach slaughter end points, but had higher total feed energy intake available for production. Steers fed corn silage diets had significantly greater energetic efficiency (P less than .05) than those fed alfalfa haylage, due to increased use of ME to produce fat in the carcass. Protein type did not influence gain, feed or energetic efficiency, energy intake, or most carcass traits. A significant protein system x forage source interaction among the four diets was detected for crossbred steers fed corn silage and fish meal, for which there was significantly greater feed conversion with lower energy intake above maintenance, possibly due to better fiber digestion and(or) amino acid flow to the lower tract. Alfalfa haylage plus soybean meal diets decreased (P less than .05) the percentage of Holsteins grading USDA Choice or higher. These results indicate that corn silage, because of greater energy concentration, was a more desirable forage in feedlot diets composed of less than or equal to 40% forage and that protein type (soybean meal and fish meal) in growing diets is not an important factor in feedlot performance or carcass traits of Holstein or crossbred steers that are fed these diets.     

补饲马铃薯藤对山羊生长性能、消化率和胴体特征的影响

本研究旨在探讨马铃薯藤饲喂水平对山羊生长性能、养分消化率和胴体特征的影响.试验将平均初始体重为(14.42±0.24)kg的40头山羊随机分为4组,每组5个重复,每个重复2头.T1组仅饲喂干草,T2组饲喂干草+100％马铃薯藤,T3组饲喂干草+50％马铃薯藤+50％浓缩料,T4组饲喂100％浓缩料.在为期10周的饲养试...