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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]

Feeding zilpaterol hydrochloride (ZH) with ruminally protected AA was evaluated in a small-pen feeding trial. Crossbred steers (n = 180; initial BW = 366 kg) were blocked by weight and then randomly assigned to treatments (45 pens; 9 pens/ treatment). Treatment groups consisted of no ZH and no AA (Cont-), ZH and no AA (Cont+), ZH and a ruminally protected lysine supplement (Lys), ZH and a ruminally protected methionine supplement (Met), and ZH and ruminally protected lysine and methionine (Lys+Met). Zilpaterol hydrochloride (8.3 mg/kg DM) was fed for the last 20 d of the finishing period with a 3-d withdrawal period. Lysine and Met were top dressed daily for the 134-d feeding trial to provide 12 or 4 g·hd-1·d-1, respectively, to the small intestine. Carcass characteristics, striploins, and prerigor muscle samples were collected following harvest at a commercial facility. Steaks from each steer were aged for 7, 14, 21, and 28 d, and Warner-Bratzler shear force (WBSF) was determined as an indicator of tenderness. Prerigor muscle samples were used for immunohistological analysis. Cattle treated with Met and Lys+Met had increased final BW (P < 0.3) and ADG (P < 0.05) compared to Cont- and Cont+. Supplementation of Lys, Met, and Lys+Met improved G:F (P < 0.05) compared to Cont- during the ZH feeding period (d 111 to 134) as well as the entire feeding period (P < 0.05). Zilpaterol hydrochloride increased carcass ADG (P < 0.05) when compared to non-ZHfed steers. Methionine and Lys+Met treatments had heavier HCW (P < 0.02) than that of Cont-. Yield grade was decreased (P < 0.04) for Cont+ steers compared to steers treated with Lys, Lys+Met, and Cont-. Tenderness was reduced (P < 0.05) with ZH regardless of AA supplementation. Lysine, Met, Lys+Met, and Cont+ had less tender steaks (P < 0.05) throughout all aging groups compared to Cont-. Steaks from Lys-treated steers were less tender (P < 0.05) than those of Cont+ during the 7- and 14-d aging periods. Nuclei density was the greatest with Cont- cattle compared to all other treatments suggesting a dilution effect of the nuclei in the larger muscle fibers with ZH feeding. Supplementation of Met in conjunction with ZH feeding increased ADG and HCW although this may lead to decreased tenderness even after aging for 28 d. These findings indicated that steers fed ZH may require additional AA absorbed from the small intestine to maximize performance. [ABSTRACT FROM AUTHOR]

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]

British x Continental heifers (n = 3,382; initial BW = 307 kg) were serially slaughtered to determine if increasing days on the finishing diet (DOF) mitigates negative consequences of zilpaterol HC1 (ZH) on quality grade and tenderness of beef. A 2 × 3 factorial arrangement of treatments in a completely randomized block design (36 pens; 6 pens/treatment) was used. Zilpaterol HC1 (8.33 mg/kg DM) was fed 0 and 20 to 22 d before slaughter plus a 3 to 5 d withdrawal to heifers spending 127, 148, and 167 DOF. Feedlot and carcass performance data were analyzed with pen as the experimental unit. Three hundred sixty carcasses (60 carcasses/treatment) were randomly subsampled, and strip loin steaks were aged for 7, 14, and 21 d for assessment of Warner-Bratzler shear force (WBSF) and slice shear force (SSF) with carcass serving as the experimental unit for analysis. No relevant ZH × DOF interactions were detected (P > 0.05). Feeding ZH during the treatment period increased ADG by 9.5%, G:F by 12.5%, carcass ADG by 33.6%, carcass G:F by 35.9%, carcass ADG:live ADG by 15.6%, HCW by 3.2% (345 vs. 356 kg), dressing percent by 1.5%, and LM area by 6.5% and decreased 12th-rib fat by 5.2% and yield grade (YG) by 0.27 units (P < 0.01). Feeding ZH tended to decrease marbling score (437 vs. 442 units; P = 0.10) and increased WBSF at 7 (4.25 vs. 3.47 kg; P < 0.01), 14 (3.57 vs. 3.05 kg; P < 0.01), and 21 d (3.50 vs. 3.03 kg; P < 0.01). Feeding ZH decreased empty body fat percentage (EBF; 29.7% vs. 30.3%; P < 0.01) and increased 28% EBF adjusted final BW (473.4 vs. 449.8 kg; P < 0.01). Analysis of interactive means indicated that the ZH × 148 DOF group had a similar percentage of USDA Prime, Premium Choice, Low Choice, and YG 1, 2, 3, 4, and 5 carcasses (P > 0.10) and decreased percentage of Select (30.4 vs. 36.6%; P = 0.03) and Standard (0.2 vs. 0.9%; P = 0.05) carcasses compared with the control × 127 DOF group. As a result of ZH shifting body composition, extending the DOF of beef heifers is an effective feeding strategy to equalize carcass grade distributions. This can be accomplished along with sustaining the ZH mediated advantages in feedlot and carcass weight gain. [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]

Melengestrol acetate (MGA) has been used in the United States for nearly 40 yr to enhance feedlot heifer performance, yet unequivocal studies have not been conducted to discover the mechanism of action. Our hypothesis was that MGA may induce various populations of muscle-derived cells (MDC) to the adipogenic pathway in both a bovine and murine cell culture model. To determine this, MDC were digested from the semimembranosus muscle tissue of six 14-mo-old crossbred steers. The addition of insulin, oleic acid, and ciglitizone (IOC) with cultured bovine MDC resulted in morphological differences compared with control cultures. Multilocular lipid droplets stained with Oil Red 0 were seen not only in single MDC, but also in fused myotubes. An increase (P < 0.05) in relative PPAR-γ messenger RNA (mRNA) levels was measured in MDC incubated with IOC. However, myogenin mRNA levels in MDC incubated with JOC were repressed (P < 0.05) compared with nontreated MDC. Cultures of MDC treated with 10 μM insulin, 10 μM oleic acid, 10 μM ciglitizone, 10 μM estradiol-17β (E2), and 10 nM IVIGA resulted in cultures with highly distributed lipid droplets not only in single cells, but also in the multinucleated myotubes. Relative C/EBPβ and PPARγ mRNA levels in total RNA isolated from MDC treated with MGA increased (P < 0.05) compared with control cultures. Estradiol treatment had no effect (P > 0.05) on these mRNA levels. The addition of both E2 and MGA to MDC increased (P < 0.05) C/EBPβ mRNA levels and tended (P = 0.06) to increase the PPAR1 mRNA level. There was no difference (P > 0.10) in relative myogenin rnRNA among the control, E2, and MGA treatments. Relative C/EBPβ, PPARγ, and myogenin mRNA levels were investigated in murine C2C12, C3H 10T 1/2, and 3T3-L1 cells. Treatment of cultures with 10 nM MGA increased C/EBPβ levels (P < 0.05) in C2C12 myoblasts and tended (P = 0.08) to increase C/EBPβ levels in 3T3-L1 preadipocytes. These data indicate that populations of cells are present in postnatal skeletal muscle that, under the appropriate stimuli in a culture model, express adipogenic genes and accumulate lipids. In addition, the synthetic progestogen MGA appeared to upregulate the genes necessary for conversion to the adipogenic pathway. [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]

The most common Salmonella serovars causing clinical disease in pigs are Salmonella enterica serovars Typhimurium (Typhimurium) and Choleraesuis. Given that the swine host-adapted serovar Choleraesuis has been reported to cause systemic disease, a different disease outcome from that of Typhimurium, our working hypothesis was that this serovar would likely engage systemic immune-inflammatory mechanisms, resulting in elevated systemic cytokine secretion. Forty-eight weaned pigs were blocked by BW and sex, and randomly allotted to 1 of 3 treatments in a 14- d study. Each treatment had 8 replicates (pens), with 2 pigs/pen. The treatments consisted of a negative control and pigs repeatedly fed 108 cfu of Typhimurium or Choleraesuis. On d 0, the pigs were fed Choleraesuis or Typhimurium in dough balls, and the bacteria were refed twice weekly throughout the experiment. Control pigs received dough balls without bacteria. All pigs were housed in temperature-controlled rooms under constant lighting and were fed a standard corn-soybean meal-based nursery diet. Pig BW and feed disappearance were used to determine ADG, ADFI, and G:F. Rectal temperatures were obtained daily from 1 pig/pen beginning 2 d before the first bacterial feeding through d 7 using rapid-response digital thermometers. Serum was collected on d 0, 7, and 14 from a single pig/pen for analysis of IGF-I, tumor necrosis factor-α , and IL-1β. There was no change in the rectal temperature of the control or the Typhimurium-challenged pigs (compared with d 0) or when comparing Typhimurium- challenged pigs with control animals. In contrast, pigs fed Choleraesuis had increased rectal temperatures beginning on d 2 and continuing through d 7 (P < 0.05), with the greatest elevation on d 3 (P < 0.001) compared with the control pigs. Average daily gain and ADFI of pigs challenged with Typhimurium did not differ from those of the control animals. Pigs fed Choleraesuis had a 25% reduction in ADG (P < 0.0001) and ADFI (P < 0.002) compared with the control pigs. On d 7, pigs fed Choleraesuis had reduced serum IGF-I compared with control (P < 0.01) or Typhimurium-challenged pigs (P = 0.01). Bacterial feeding did not affect serum tumor necrosis factor-α or IL-1β compared with control pigs at any time throughout the experiment. We conclude that repeated exposure of weaned pigs to Choleraesuis reduced growth performance in the absence of changes in systemic inflammatory cytokines. [ABSTRACT FROM AUTHOR]

In vitro experiments were performed to investigate the effects of melengestrol acetate (MGA) or progesterone (P4) on bovine muscle satellite cells and C2C12 myoblasts. Addition of MGA at physiological and supraphysiological concentrations resulted in a dose-dependent decrease (P < 0.05) in DNA synthesis as measured by ³H] -thymidine incorporation (TI). Similarly, P4 addition (0.01 nM) reduced (P < 0.05) TI. Addition of MGA (10 nM) increased (P < 0.05) IGF-I mRNA abundance but did not affect myogenin mRNA. Progesterone addition (10 nM) increased myogenin mRNA abundance (P < 0.05). In C2C12 cultures, P4 addition resulted in a dose-dependent decrease in TI. The anti- progestin RU486, in combination with MGA or P4, also resulted in reduced (P < 0.05) TI. Treatment with RU486 alone had a negative effect (P < 0.05) on TI that was similar to the progestins. Treatment of C2C12 myoblasts with MGA (100 nM) resulted in an increase (P < 0.05) in myogenin mRNA. These studies suggest that progestins may reduce satellite cell proliferation, ultimately affecting carcass composition. [ABSTRACT FROM AUTHOR]

Vitamin D3 (D3) supplementation may be used to increase tenderness in beef from cattle fed zilpaterol hydrochloride (ZH). The study was arranged as a 2 × 2 factorial with fixed effects of ZH (no ZH or ZH fed at 8.3 mg/kg DM for 20 d with a 3-d withdrawal) and D3 (no D3 or 500,000 IU D3∙steer-1∙d-1 for 10 d prior to harvest). Cattle (n = 466) were harvested in 2 blocks on the basis of BW with subsequent collection of carcass data. Full loins and inside rounds (n = 144 of each subprimal) were collected for fabrication of 5 steaks from the longissimus lumborum (LL), gluteus medius (GM), and semimembranosus (SM), which were aged for 7, 14, 21, 28, or 35 d. Warner-Bratzler shear force (WBSF) was used to evaluate mechanical tenderness of LL, GM, and SM steaks at all aging periods. Slice shear force (SSF) analysis was conducted on only 14- and 21-d LL steaks. No interactions (P > 0.05) between ZH and D3 occurred throughout the entire study. Supplementing ZH resulted in increased HCW (P < 0.01), larger LM area (P < 0.01), and improved calculated yield grades (P < 0.01) with decreases in fat thickness (P = 0.02) and marbling scores (P = 0.05). Supplementation with D3 increased calculated yield grade (P < 0.01) and decreased (P = 0.01) rib eye area. Feeding ZH increased (P ≤ 0.05) WBSF of LL steaks at each postmortem age interval, whereas D3 had no effect (P > 0.05) on WBSF or SSF of LL steaks. Like for WBSF, ZH supplementation increased SSF values at 14 and 21 d postmortem (P < 0.01) compared with those for non-ZH steaks. There was an interaction between ZH and postmortem age (P < 0.01) for WBSF of LL steaks. At 7 d LL steaks from ZH steers sheared over 0.6 kg greater than non-ZH steaks; however, by 21 d this difference was reduced to an average of 0.2 kg. Differences in distribution between LL steaks below 3.0 kg from non-ZH and ZH-fed cattle were also notable (P ≤ 0.05) through 21 d of aging. At 35 d postmortem a high proportion of LL steaks (68.5%) from ZH-fed steers required less than 3.0 kg to shear. Supplementation with ZH and D3 had no impact (P > 0.05) on WBSF values of GM steaks. Feeding ZH did not alter WBSF of SM steaks, but at 28 d D3 increased (P = 0.04) WBSF values. Shear force in ZH steaks was not effectively reduced by feeding D3 for 10 d to steers prior to harvest. Aging, however, was an effective method of reducing initially greater shear force values in LL steaks and, to a lesser degree, GM steaks from ZH-fed cattle. [ABSTRACT FROM AUTHOR]