Effects of feeding dry-rolled corn-based diets with and without wet distillers grains with solubles and zilpaterol hydrochloride on performance, carcass characteristics, and heat stress in finishing beef steers1

Abstract

Zilpaterol hydrochloride (ZH) has been approved for use since 2006; however, there is no research on any interactions between ZH and coproducts. Additionally, there is no published information on the potential effects of ZH on heat stress in feedlot cattle. Therefore, an experiment was conducted to determine the effects of feeding dry-rolled corn (DRC)-based diets with and without wet distillers grains with solubles (WDGS) and ZH on performance, carcass characteristics, and heat stress in feedlot cattle. Four hundred thirty-eight steers were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments in 16 pens with 26 to 28 steers in each pen. Factors consisted of inclusion of 0 or 30% (on a DM basis) WDGS and inclusion of ZH at 0 or 84 mg/steer daily for 21 d at the end of the finishing period. Therefore, cattle were blocked by BW and randomly assigned to 1 of the resulting 4 treatment combinations: 1) DRC-based diet with 0% WDGS and 84 mg/steer ZH, 2) DRC-based diet with 0% WDGS and no ZH, 3) DRC-based diet with 30% WDGS and 84 mg/steer of ZH, and 4) DRC-based diet with 30% WDGS and no ZH. Final live BW, carcass-adjusted BW, ADG, and G:F were greater for cattle fed ZH than non-ZH-fed cattle (P < 0.01). Additionally, cattle fed ZH consumed 7.4% less DM than cattle not fed ZH (P < 0.01). Cattle fed ZH for 21 d also had a 2.9% greater HCW (P < 0.01), a 1.1% greater dressing percentage (P < 0.01), 7.3% greater LM area (P < 0.01), and an 8.4% improvement in yield grade (P < 0.01) than cattle not fed ZH. For the main effect of WDGS inclusion, ADG was greater for cattle fed 0 vs. 30% WDGS (P = 0.04) and G:F also tended to be greater for cattle fed 0 vs. 30% WDGS (P = 0.07) for the 21-d ZH feeding period. However, when evaluated over the entire experiment, cattle fed 30 vs. 0% WDGS had a greater ADG and G:F (P < 0.01). Furthermore, cattle fed 30 vs. 0% WDGS had a greater dressing percentage and tended to have a greater amount of 12th rib fat (P < 0.07). Heat stress measurements were collected during the time cattle were fed ZH, from May 31 to July 12, 2013. The slopes for change in respiration rate and panting score per day were positive but were not different across dietary treatments (P > 0.71); in addition, the slopes for change in respiration rate and panting score when accounting for environmental conditions were positive but were not different across dietary treatments (P > 0.32).

Review of proposed MRLs, safety evaluation of products obtained from animals treated with zilpaterol and evaluation of the effects of zilpaterol on animal health and welfare

“…Hales et al. () did not find a significant effect of zilpaterol on respiration rate (p = 0.12; adjusted for climate p = 0.68) or panting score (p = 0.64; adjusted for climate p = 0.29), while Boyd et al. (), found that cattle fed zilpaterol had greater respiration rates than cattle fed the control diet (p < 0.05), and a tendency to have a greater panting score (p = 0.1) than the control cattle.…”

“…In Hales et al. () study with 438 steers, treatment combinations were 0 and 84 mg zilpaterol/animal per day with two different diets. Animals were distributed in four pens/treatment (26–28 animals/pen).…”

“…Three similar studies (2 9 2 factorial experimental design) were performed in male beef cattle (steers) fed with zilpaterol during the 21 days before slaughter with a 3-4 days withdrawal period. Cattle received an implant with different composition depending on the study (trenbolone acetate and estradiol or tylosine) (Hales et al, 2014;Maxwell et al, 2014 andBoyd et al, 2015). In Hales et al (2014) study with 438 steers, treatment combinations were 0 and 84 mg zilpaterol/animal per day with two different diets.…”

“…Cattle received an implant with different composition depending on the study (trenbolone acetate and estradiol or tylosine) (Hales et al, 2014;Maxwell et al, 2014 andBoyd et al, 2015). In Hales et al (2014) study with 438 steers, treatment combinations were 0 and 84 mg zilpaterol/animal per day with two different diets. Animals were distributed in four pens/treatment (26-28 animals/pen).…”

“…In the study of Maxwell et al (2014), 160 steers were supplemented or not with 90 mg zilpaterol/animal per day and mortality and lameness were recorded. Hales et al (2014) did not find a significant effect of zilpaterol on respiration rate (p = 0.12; adjusted for climate p = 0.68) or panting score (p = 0.64; adjusted for climate p = 0.29), while Boyd et al (2015), found that cattle fed zilpaterol had greater respiration rates than cattle fed the control diet (p < 0.05), and a tendency to have a greater panting score (p = 0.1) than the control cattle. In the same study, there was a tendency (p = 0.06) for cattle fed zilpaterol to have a lesser proportion of cattle that scored 0 (normal mobility) and 1 (slightly stiff gait) than the cattle in the control group at the point where cattle were going to the restrainer.…”