202
Effects of shade and feeding zilpaterol hydrochloride to finishing steers on performance, carcass quality, mobility, and body temperature
Crossbred steers (n=480) were utilized to study the effects of shade and feeding zilpaterol hydrochloride (ZH) on performance, carcass quality, mobility, and body temperature (BT). A randomized block design with a 2×2 factorial arrangement of treatments was conducted with four replicates per treatment. Factors included housing type (open lot or shaded pens; HT) and the use of ZH or not during the last 21 days of the finishing period. Cattle were blocked into heavy or light BW and assigned randomly to pens within block. Boluses to record BT were inserted prior to initiation of ZH feeding. Respiration rates were taken daily during the ZH feeding period. Mobility scores were collected at various time points from before ZH feeding through harvest. For carcass and performance data, the model included fixed effects of block, dietary treatment, HT and their interaction. For mobility, respiration, and BT day was included as a repeated measure using either simple (mobility and BT) or autoregressive (respiration) covariance structure. Mobility included a covariate of mobility score prior to treatment. Interactions between ZH and HT were not significant (P>0.26). No differences (P>0.44) were observed for DMI, ADG, or G:F on a live basis due to ZH but cattle fed in open lots tended (P=0.11) to gain more than cattle with shade. Carcasses were 14 kg heavier with larger LM area (P<0.01) for cattle fed ZH. Respiration rates for cattle fed ZH were greater (P=0.05) with no differences (P=0.88) due to HT. Mobility scores tended (P=0.08) to be greater (worse mobility) for cattle fed ZH and time was significant (P<0.01) with observations taken the morning of harvest at the abattoir being the worst for all cattle. An interaction (P<0.01) was observed between ZH and HT for BT. Control cattle in shade had lower (P<0.05) average and maximum BT than control cattle in open pens. Cattle in shade fed ZH had greater (P<0.05) average and maximum BT than cattle fed ZH in open pens. In open pens, cattle fed ZH had lower (P<0.05) area under the curve (AUC) BT than the control. In shaded pens, no difference (P>0.05) was observed in AUC due to ZH but, average and maximum BT was greater (P<0.05) for cattle fed ZH. Feeding ZH increased respiration rate and slightly increased BT. Feeding ZH also increased carcass weight with a minor impact on mobility. USDA is an equal opportunity provider and employer.
Keywords: Mobility, Temperature, Zilpaterol hydrochloride