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British x Continental steers (n = 168; 7 pens/treatment; initial BW = 362 kg) were used to evaluate the effect of dose/payout pattern of trenbolone acetate (TBA) and estradiol-17β (E2) and feeding of zilpaterol hydrochloride (ZH) on serum urea-N (SUN), NEFA, IGF-I, and E2 concentrations and LM mRNA expression of the estrogen (ER), androgen (ANR), IGF-1 (IGF-IR), β 1-adrenergic (β 1-AR), and β 2-adrenergic (β 2-AR) receptors and IGF-I. A randomized complete block design was used with a 3 x 2 factorial arrangement of treatments. Main effects were implant (no implant [NI], Revalor-S [REV-S; 120 mg TBA + 24 mg E2], and Revalor-XS [REV-X; 200 mg TBA + 40 mg E2]) and ZH (0 or 8.3 mg/kg of DM for 20 d with a 3-d withdrawal). Steers were fed for 153 or 174 d. Blood was collected (2 steers/pen) at d-1,2, 6, 13, 27, 55, 83, 111, and 131 relative to implanting; LM biopsies (1 steer/ pen) were collected at d -1, 27, 55, and 111. Blood and LM samples were collected at d -1, 11, and 19 relative to ZH feeding. A greater dose of TBA + E2 in combination with ZH increased ADG and HCW in an additive manner, suggesting a different mechanism of action for ZH and steroidal implants. Implanting decreased (P < 0.05) SUN from d 2 through 131. Feeding ZH decreased (P < 0.05) SUN. Serum NEFA concentrations were not affected by implants (P = 0.44). There was a day x ZH interaction (P = 0.06) for NEFA; ZH steers had increased (P < 0.01) NEFA concentrations at d 11 of ZH feeding. Serum E2 was greater (P < 0.05) for implanted steers by d 27. Serum trenbolone-17β was greater (P < 0.05) for implanted steers by d 2 followed by a typical biphasic release rate, with a secondary peak at d 111 for REV-X (P < 0.05) implanted steers. Implanting did not affect mRNA expression of the ANR or ER, but the IGF-IR and the β 1-AR and β 2-AR were less (P < 0.05) for REV-S than NI at d 55 and β 2-AR mRNA was less (P < 0.05) for REV-S than for REV-X. Expression of the IGF-IR and the β 1-AR at d 111 was greater (P < 0.05) for REV-X than for REV-S and NI at d 111, and the P2-AR was less (P < 0.05) for REV-S than for REV-X. Feeding ZH did not affect mRNA expression of the β 1-AR and β 2-AR. Both implanting and feeding ZH decreased SUN, but a greater dose of TBA + E2 did not result in further decreases. In addition, feeding ZH increased serum NEFA concentrations. Metabolic changes resulting from implanting and feeding ZH may aid in explaining steer performance and carcass responses to these growth promotants. [ABSTRACT FROM AUTHOR]

Four experiments evaluated the effect of implant dose and release pattern on performance and carcass traits of crossbred beef steers. In Exp. 1, steers (4 to 7 pens/treatment; initial BW = 315 kg) were fed an average of 174 ci. Treatments were 1) no implant (NI); 2) Revalor-S [120 mg of trenbolone acetate (TBA) and 24 mg of estradiol 17f3 (E2); REV-SI; 3) Revalor-IS followed by REV-S (cumulatively 200 mg of TBA and 40 mg of E2 reimplanted at 68 to 74 d; REVIS/S); and 4) Revalor-XS (200 mg of TBA and 40 mg of E2 REV-X), Carcass-adjusted final BW was greater (P < 0.05) for REV-X and REV-IS/S than for REV-S (610, 609, and 598 kg, respectively). Daily DM1 did not differ (P > 0.10) among the 3 implants, but carcassadjusted G:F was greater (P < 0.05) for REV-X and REV-IS/S than for REV-S (0.197 and 0.195 vs. 0.188). Both HCW and LM area were greater (P < 0.05) for REV-X and REV-IS/S than for REV-S. Marbling scores were greatest (P < 0.05) for REV-S and least (P < 0.05) for REV-IS/S; REV-X was intermediate to NI and REV-IS/S. In Exp. 2, steers (10 pens/treatment; initial BW = 391 kg) were fed 131 d, with treatments of REV-S, REV-IS/S (reimplanted at 44 to 47 d), and REV-X. Carcass-adjusted final BW (598 kg), ADG (1.6 kg), DM1 (9.4 kg), G:F (0.17), and HCW did not differ (P > 0.10) among treatments. The percentage of Choice was less (P < 0.05) and percentage of Select greater (P < 0.05) for REV-IS/S than for REV-S and REV-X. In Exp. 3, steers (10 pens/treatment; initial BW = 277 kg) were fed 197 d aud received either REVIS/S (reimplanted at 90 to 103 cI) or REV-X. Carcassadjusted final BW (625 vs. 633 kg) and ADG (1.81 vs. 1.76 kg) were greater (P < 0.05) for REV-X-implantecl steers. Daily DM1 did not differ, but G:F tended (P < 0.10) to be increased and HCW was greater (P < 0.05) for REV-X than for REV-IS/S. In Exp. 4, steers (8 pens/treatment; initial BW = 238 kg) were fed 243 d and received either REV-IS/S (reimplanted at 68 to 71 d) or REV-X. Carcass-adjusted final BW (612 kg), ADG (1.54 kg), DM1 (7.55), and G:F (0.21) did not differ (P > 0.10) for REV-IS/S and REV-X-implanted steers. Carcass traits did not differ among implants, but the percentage of Choice carcasses was greater (P < 0.05) and percentage of Select was less (P < 0.05) for REV-X than for REV-IS/S. These data indicate that when TBA/E2 dose is equal, the altered release rate of REV-X can improve performance and quality grade, but these effects depend on duration of the feeding period and timing of initial and terminal implants. [ABSTRACT FROM AUTHOR]

Our objectives were to evaluate the dose/payout pattern of trenbolone acetate (TBA) and estradiol-1713 (E2) implants and feeding of zilpaterol hydrochloride (ZH) on performance and carcass characteristics of finishing beef steers. A randomized complete block design was used with a 3 × 2 factorial arrangement of treatments. British × Continental steers (n = 168; initial BW = 362 kg) were blocked by BW and allotted randomly to 42 pens (7 pens/treatment; 6 pens/ block; 4 steers/pen). The main effects of treatment were implant [no implant (NI); Revalor-S (REV-S; 120 mg of TBA + 24 mg of E2); and Revalor-XS (REV-X; 200 mg of TBA + 40 mg of E2)I and ZH (0 or 8.3 mg/ kg of DM for 20 d with a 3-d withdrawal before slaughter). Blocks were split into 2 groups, and block groups were fed for either 153 or 174 d. No implant × ZH interactions were noted for cumulative performance data. Overall, shrunk final BW (567, 606, and 624 kg for NI, REV-S, and REV-X, respectively), ADG (1.25, 1.51, and 1.60 kg), and G:F (0.14, 0.16, and 0.17) increased (P < 0.05) as TBA and E2 dose increased. Implanting increased (P < 0.05) DM1, but DM1 did' not differ (P > 0.10) between REV-S and REV-X (8.8 for NI vs. 9.4 kg/d for the 2 implants). From d ito 112 of the feeding period, implanting increased (P < 0.05) ADG and G:F, but REV-S and REV-X did not differ (P> 0.10). From d 112 to end, ADG increased by 19% (P < 0.05) and G:F was 18% greater (P < 0.05) for REV-X vs. REVS. Carcass-adjusted final BW (29-kg difference), ADG (0.2-kg/d difference), and G:F (0.02 difference) were increased (P < 0.05) by ZH, but daily DM1 was not affected by feeding ZH. Hot carcass weight was increased (P < 0.05) by ZH (19-kg difference) and implant, with REV-X resulting in the greatest response (HCW of 376 for NI vs. 404 and 419 kg for REV-S and REV-X, respectively; P < 0.05). An implant x ZH interaction (P = 0.05) occurred for dressing percent (DP). Without ZH, implanting increased DP, but DP did not differ (P > 0.10) between REV-X and REV-S. With ZH, REV-X increased (1.7%; P < 0.05) DP vs. NI and REV-S. Marbling score, 12th-rib fat, and KPH were not affected (P > 0.10) by implant or ZH. Overall, treatment increased steer performance and HCW in an additive fashion, suggesting different mechanisms of action for ZH and steroidal implants. In addition, a greater dose of TBA + E2 and extended payout improved steer performance and HCW. [ABSTRACT FROM AUTHOR]

This experiment evaluated the dose and payout pattern of trenbolone acetate (TBA) and estradiol-17β (E2) on LM mRNA expression of adenosine monophosphate-activated protein kinase-ɑ (AMPK-ɑ), C/EBPβ, G protein-coupled receptor 41(GPR41), G protein-coupled receptor 43 (GPR43), PPARγ, and stearoyl CoA desaturase (SCD) in finishing feedlot steers as indicators of adipogenesis and marbling development. British · Continental steers (n = 168; 14 pens/treatment; initial BW = 362 kg) were used in a randomized complete block design. Treatments included: no implant (NI), Revalor-S (REV-S; 120 mg TBA + 24 mg E2), or Revalor-XS (REV-X; delayed release implant: 80 mg TBA + 16 mg E2 [uncoated], 120 mg TBA + 24 mg E2 [coated], 200 mg TBA + 40 mg E2 [total]). Steers were fed 1 time daily for an average of 164 d. The LM biopsies were collected (1 steer/pen) on d -1, 27, 55, and 111 relative to timing of implant. Total RNA was isolated from each sample and real-time quantitative PCR was used to measure quantity of AMPK-ɑ, C/EBPβ, GPR41, ,it, PPARγ, and SCD mRNA. No implant · day interactions were detected (P ≥ 0.19) in this experiment. Day impacted the mRNA expression of all adipogenic genes (P ≤ 0.02). The main effect of implant tended (P = 0.09) to influence expression of AMPK-ɑ, REV-X had an 8.8% increase over NI and an 18.7% increase over REV-S. Implant influenced (P = 0.03) mRNA expression of GPR41, expression of GPR41 for the REV-X treatment was not different (P > 0.10) from NI, and both were greater (P ≤ 0.05) than REV-S (1.13, 1.00, and 0.67 ± 0.224 arbitrary units) for REV-X, NI, and REV-S, respectively. Implant also influenced (P = 0.02) expression of GPR43, expression of GPR43 for REV-X was not different (P > 0.10) from NI, and both were greater (P ≤ 0.05) than REV-S (1.27, 1.07, and 0.72 ± 0.234 arbitrary units) for REV-X, NI, and REV-S, respectively. Implant influenced (P = 0.02) mRNA expression of PPARγ in LM tissue, expression of PPARγ for REV-X was not different (P > 0.10) from NI, and both were greater (P ≤ 0.05) than REV-S (1.09, 1.02, and 0.69 ± 0.195 arbitrary units) for REV-X, NI, and REV-S, respectively. The REV-X steers received the greatest anabolic dose of TBA + E2 without detriment to marbling scores. The increased mRNA expression of adipogenic genes for REV-X steers suggest that the delayed and gradual release of anabolic stimulants associated with REV-X might have mitigated decreases in marbling generally attributed to multiple combined TBA + E2 implants. [ABSTRACT FROM AUTHOR]

Urea kinetics were measured in 2 experiments, with treatments designed to change protein deposition by the animal. Our hypothesis was that increased protein deposition by cattle (Bos taurus) would reduce urea production and recycling to the gastrointestinal tract. Urea kinetics were measured by continuous intravenous infusion of 15N15N-urea followed by measurement of enrichment in urinary urea at plateau. In Exp. 1, 6 steers (139 kg) were maintained in a model in which leucine was the most limiting AA. Treatments were arranged as a 2 x 3 factorial and were provided to steers in a 6 x 6 Latin square design. Leucine treatments included 0 or 4 g/d of abomasally supplemented L-leucine, and energy treatments included control, abomasal glucose infusion (382 g DM/d), or ruminal VFA infusion (150 g/d of acetic acid, 150 g/d of propionic acid, and 50 g/d of butyric acid). Leucine supplementation increased (P < 0.01) N retention, and energy supplementation tended to increase (P = 0.09) N retention without differences between glucose and VFA supplements (P = 0.86). Energy supplementation did not strikingly improve the efficiency of leucine utilization. Although both leucine and energy supplementation reduced urinary urea excretion (P ≤ 0.02), treatments did not affect urea production (P ≥ 0.34) or urea recycling to the gut (P ≥ 0.30). The magnitude of change in protein deposition may have been too small to significantly affect urea kinetics. In Exp. 2,6 steers (168 kg) were maintained in a model wherein methionine was the most limiting AA. Steers were placed in 2 concurrent 3x3 Latin squares. Steers in one square were implanted with 24 mg of estradiol and 120 mg trenbolone acetate, and steers in the other square were not implanted. Treatments in each square were 0,3, or 10 g/d of L-methionine. Implantation numerically improved N retention (P=0.13) and reduced urea production rate (P = 0.03), urinary urea excretion (P < 0.01), and urea recycling to the gastrointestinal tract (P = 0.14). Effects of methionine were similar to implantation, but smaller in magnitude. When protein deposition by the body is increased markedly, ruminally available N in the diet may need to be increased to offset reductions in urea recycling. [ABSTRACT FROM AUTHOR]

Twenty crossbred yearling steers (421 kg) were used to evaluate the effects of implanting with trenbolone acetate (TBA; 120 mg), estradiol-17β (E2; 25.7 mg), and a combination (120 mg of TBA and 24 mg of E2) on adipogenic and myogenic mRNA concentrations. Animals were blocked by BW and within each block were assigned to 1 of 4 treatments. Animals were housed and fed in individual pens with 5 animals per treatment. All animals were weighed weekly, and muscle biopsy samples were taken from the LM of each steer on d 0 (before implantation), 7, 14, and 28. Total RNA was isolated from each sample and real-time quantitative PCR was used to measure the quantity of C/EBPβ, PPARγ, stearoyl CoA desaturase (SCD), myogenin, and 3 isoforms of bovine myosin heavy chain (MHC) mRNA. Total BW gain from the 28-d period was adjusted to d 0 by use of covariant analysis, and steers in the implant groups tended (P = 0.09) to have increased BW gain compared with nonimplanted control steers. Analysis of the gene expression of MHC showed that neither implant nor day (P > 0.20) had a significant effect on the expression of type I or IIX MHC mRNA There was also no treatment effect (P > 0.20) on MHC-IIA and myogenin, but increasing days on feed increased (P = 0.05) the expression of MHC-IIA mRNA. Relative mRNA abundance of C/EBPβ, PPARγ, and SCD increased (P < 0.05) during days of feed but PPARγ decreased (P < 0.05) with the treatment of combined TBA/E2 implant. Results of this study indicate that implanting with TBA, E2, or both increased BW gain and decreased adipogenic gene expression of finishing steers without significantly affecting the concentration of type I, IIA, or IIX MHC mRNA. Increasing days on feed increased both MHC-IIA and adipogenic gene expression in bovine skeletal muscle biopsy samples. We conclude that administration of steroidal implants had no effect on the proportion of the 3 MHC mRNA isoforms but decreased C/EBPβ, PPARγ, and SCD mRNA in bovine skeletal muscle. [ABSTRACT FROM AUTHOR]

Our objectives were to determine the effects of zilpaterol hydrochloride (ZH) and the release rate of trenbolone acetate and estradiol-17ß on Warner-Bratzler shear force (WBSF) and slice shear force (SSF) of longissimus lumborum (LL) and the WBSF of gluteus medius (GM) and psoas major (PM) in response to various aging periods. British × Continental steers (n = 168) were assigned to treatments in a 3 × 2 factorial. The main effects of treatment were implant [no implant (NI); Revalor-S (REV-S), Revalor-XS (REV-XS)] and ZH (0 or 8.3 mg/kg of DM for 20 d). Harvest group was included as a random effect to account for the variation in days on feed (153 or 174 d). Loins (n = 96) were fabricated to obtain strip loin, top sirloin butt, and tenderloin subprimals. Five 2.54-cm steaks were cut from each subprimal and assigned to 1 of 5 aging periods (7, 14, 21, 28, or 35 d postmortem). Feeding ZH increased (P < 0.01) LL WBSF and SSF values at each aging period compared to controls. Implanting increased (P < 0.05) LL WBSF values at 14 and 21 d, but did not affect LL SSF values (P > 0.05). Only REV-S increased WBSF values at 28 and 35 d compared to NI or REV-XS. The percentage of LL steaks with a WBSF value < 4.6 kg did not differ (P > 0.05) between ZH supplementation or implant strategy at any aging period, and by d 28 over 99% of LL steaks registered WBSF values < 4.6 kg. Feeding ZH increased (P < 0.05) GM WBSF values only on d 21. Implant had no effect (P > 0.05) on GM WBSF values. The percentage of GM steaks with a WBSF value < 4.6 kg did not differ (P > 0.05) between ZH supplementation or implant strategy at any aging period. Neither ZH nor implant strategy affected PM WBSF values (P > 0.05). All PM WBSF values were < 4.6 kg on d 7. The results of this study indicated feeding ZH increased WBSF and SSF of LL steaks, regardless of aging period; however, the percentage of steaks with WBSF < 4.6 kg did not differ due to ZH or implant. Implanting increased LL WBSF, but not SSF values. These results showed although differences existed between implanting, as well as ZH supplementation of British × Continental steers, 99% of LL steaks were classified as tender based on WBSF values by extending aging to 28 d postmortem. It should be noted that 21.2% of 7 d, 13.8% of 14 d, and 17.3% of 21 d ZH steaks had WBSF values > 4.6 kg, but 0% of non-supplemented steaks were > 4.6 kg at these aging periods. However, because ZH and implants can increase retail yield of valuable subprimals such as the tenderloin, considerable value could be captured through ZH supplementation with anabolic implants since shear force was not affected in PM steaks. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate the effects of wet distillers grains plus solubles (DG) and roughage source on finishing cattle performance, carcass characteristics, and in vitro fermentation. In Exp. 1, crossbred beef steers (n = 224, initial BW = 349 kg) were used in a randomized complete block design with a 2 × 3 + 1 factorial arrangement of treatments. Experimental diets were a standard steam-flaked corn (SFC)-based control (no DG and 10% alfalfa hay), and either 15 or 30% DG (DM basis) with roughage sources of alfalfa hay (15-AH and 30-AH), Coastal bermudagrass hay (15-BG and 30-BG), or sorghum silage (15-SS and 30-SS). Within each DG concentration, roughages provided an equivalent percentage of NDF to 7.5% AH. Steers consuming 15% DG had greater (P < 0.04) final BW, ADG, and G:F than those fed 30% DG. Feeding AH as the roughage source with DG resulted in decreased final shrunk BW and ADG (P < 0.02) compared with BG and SS. Feeding SS as the roughage source decreased (P = 0.01) G:F relative to BG. Hot carcass weight was greater (P < 0.01) for steers consuming 15 vs. 30% DG, tended to be least for diets with AH as the roughage source (P = 0.06), and did not differ for the control vs. the other diets (P = 0.86). Control cattle had an increased (P = 0.05) proportion of USDA Choice or greater carcasses compared with the average of the other treatments. In Exp. 2, the same 2 × 3 +1 factorial arrangement as in Exp. 1 was used to examine the effects of roughage source and DG on IVDMD, culture fluid osmolality, and gas production kinetics. In vitro DMD tended (P < 0.09) to be greater for BG compared with SS at 6 and 36 h of incubation and was greater for AH vs. the mean of BG and SS at 18 h (P = 0.01). Culture fluid osmolality, asymptotic maximal gas production, fractional rate of gas production, and lag time of gas production did not differ among treatments (P > 0.14). Overall, feeding 15% DG in SFC-based diets increased ADG, BW, and HCW relative to 30% DG. In addition, feeding AH tended to decrease ADG, final BW, and HCW relative to the other 2 roughage sources, whereas BG improved G:F over SS. These data suggest that including the smaller amount of DG and BG as the roughage source resulted in improved performance relative to other combinations, and that substituting roughages on the basis of equivalent NDF concentration might not be ideal for optimizing performance when feeding SFC-based finishing diets that contain DG. [ABSTRACT FROM AUTHOR]

We previously showed that a combined trenbolone acetate (TBA)/estradiol-17β (E2) implant significantly increases IGF-I mRNA levels in the LM of feedlot steers by 28 d after implantation. Here we compare the effects of E2 (25.7 mg), TBA (120 mg), and combined TBA (120 mg)/E2 (24 mg) implants on IGF-I, ICF-I receptor (IGFR-1), estrogen receptor (ER)-α and androgen receptor (AR) mRNA levels in the LM of steers. Twenty yearling crossbred steers with an average initial BW of 421.1 ± 3.6 kg were stratified by BW and randomly assigned to 1 of 4 treatments: 1) nonimplanted, control; 2) implanted with TBA and E2; 3) implanted with E2; or 4) implanted with TBA. Steers were weighed weekly starting on d 0, and muscle biopsy samples were taken from each steer on d 0 (before implantation), 7, 14, and 28. Ribonucleic acid was prepared from each sample and real-time reverse transcription-PCR was used to determine the levels of IGF-I, IGFR-1, ER-α, and AR mRNA. Body weight of implanted steers, adjusted by using d-0 BW as a covariant, tended (P = 0.09) to be greater than that of control steers. On d 7 and 28, IGF-I mRNA levels were greater (58 and 78%, respectively; P < 0.009) in E2-implanted animals than in control steers. Similarly, on d 28 the LM IGF-I mRNA level was 65% greater (P = 0.017) in TBA/E2-implanted steers than in control animals. In contrast, the TBA implant did not increase (P = 0.99) LM IGF-I mRNA levels after 28 d of implantation. Muscle IGFR-1, AR, and ER-α mRNA levels were not different (P > 0.47) in any of the treated groups compared with the control group. These data suggest that E2 is responsible for the increased muscle ICF-I mRNA level observed in steers implanted with a combined TBA/E2 implant. [ABSTRACT FROM AUTHOR]