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

Authors: BOYD, BRADLEY - University Of Nebraska; Shackelford, Steven; Hales Paxton, Kristin; Brown-Brandl, Tami; BREMER, M - University Of Nebraska; SPANGLER, M - University Of Nebraska; Wheeler, Tommy; King, David - Andy; ERICKSON, GALEN - University Of Nebraska

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2015
Publication Date: 12/3/2015
Publication URL: https://handle.nal.usda.gov/10113/61721
Citation: Boyd, B.M., Shackelford, S.D., Hales, K.E., Brown-Brandl, T.M., Bremer, M.L., Spangler, M.L., Wheeler, T.L., King, D.A., Erickson, G.E. 2015. Effects of shade and feeding zilpaterol hydrochloride to finishing steers on performance, carcass quality, heat stress, mobility, and body temperature. Journal of Animal Science. 93(12):5801-5811. doi: 10.2527/jas2015-9613.

Interpretive Summary: Zilpaterol hydrochloride is fed to cattle at the end of the finishing period to increase protein deposition in the carcass. Steers were used to study the effects of shade and feeding zilpaterol hydrochloride on performance, carcass quality, heat stress, mobility, and body temperature. Factors included housing type (open or shaded pens) and the feeding of zilpaterol hydrochloride the last 21 days with a 4-day withdrawal at the end of the feeding period. Respiration rate and panting score were collected daily during the time zilpaterol hydrochloride was fed. Mobility scores were collected at various time points from before zilpaterol hydrochloride feeding through harvest. No differences were observed for feed intake, average daily gain, or feed efficiency due to zilpaterol hydrochloride; however, cattle fed in open pens had a greater average daily gain than cattle fed in shaded pens. Cattle fed zilpaterol hydrochloride had heavier carcasses with larger ribeye area than control cattle. Respiration rates for cattle fed zilpaterol hydrochloride were greater. Time was significant for mobility scores with observations taken the morning of harvest, at the abattoir, being the worst for all groups of cattle. From these results, we interpret that zilpaterol hydrochloride improved carcass characteristics with little impact on heat stress or mobility suggesting that animal welfare was not affected by feeding zilpaterol hydrochloride for 21 days at the end of the feeding period.

Technical Abstract: 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.