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Effects of shade and feeding zilpaterol hydrochloride to finishing steers on performance, carcass quality, mobility, and body temperature

B. M. Boyd, S. D. Shackelford, K. E. Hales, T. M. Brown-Brandl, M. L. Bremer, M. L. Spangler, T. L. Wheeler, D. A. King, G. E. Erickson
Journal of animal science 2015 v.93 no.12 pp. 5801-5811
animal pens, animal performance, animal welfare, beta-adrenergic agonists, body temperature, carcass quality, cattle housing, covariance, finishing, heat stress, model validation, nutritional intervention, respiratory rate, rumen, shade, slaughterhouses, steers
Steers (n = 480) were used to study the effects of shade and feeding zilpaterol hydrochloride (ZH) on performance, carcass quality, heat stress, mobility, and body temperature (BT). A randomized block design with a 2 × 2 factorial arrangement of treatments was used with 4 replicates per treatment. Factors included housing type (open or shaded pens) and the feeding of ZH (0 or 8.33 mg/kg DM) the last 21 d on feed with a 3-d withdrawal. Cattle were blocked by BW into a heavy or light block and assigned to pen within each block. Rumen boluses to record BT were inserted prior to ZH feeding. Respiration rate and panting score were collected daily during the ZH feeding period. Mobility scores were collected at various time points from before ZH feeding through harvest. The model for performance and carcass data included the fixed effects of block, dietary treatment, housing type, and their interaction. For mobility, respiration and panting, chute exit speed, and BT, day was included as a repeated measure using a simple (mobility and BT), autoregressive (respiration) or unstructured (chute exit speed) covariance structure. Interactions between ZH and housing type were not significant (P > 0.26) for animal performance, carcass characteristics, and respiration or panting score. No differences (P > 0.44) were observed for DMI, ADG, or G:F on a live basis due to ZH; however, cattle fed in open pens tended (P = 0.08) to have a greater ADG than cattle in shaded pens. Cattle fed ZH had 14 kg heavier carcasses with larger LM area (P < 0.01) than control cattle. Respiration rates for cattle fed ZH were greater (P = 0.05) with no differences (P = 0.88) due to housing. However, time was significant (P < 0.01) for mobility scores with observations taken the morning of harvest, at the abattoir, being the worst for all groups of cattle. An interaction (P < 0.01) was observed between ZH and housing for BT. Cattle fed ZH in open pens had lower (P < 0.05) average, maximum, and area under the curve BT than control cattle in open pens. Cattle fed ZH in shaded pens had greater (P < 0.05) average and maximum BT than cattle fed ZH in open pens. In shaded pens, average and maximum BT was greater (P < 0.05) for cattle fed ZH compared to control cattle. From these results we interpret that ZH improved carcass characteristics with little impact on heat stress or mobility suggesting that animal welfare was not affected by feeding ZH for 21 d at the end of the feeding period.