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Evaluation of objective and subjective mobility variables in feedlot cattle supplemented with zilpaterol hydrochloride
The objective of this study was to examine the effects of zilpaterol hydrochloride (ZH) on mobility in feedlot cattle. Black-hided steers and heifers (n=96) were sourced from a commercial feedlot and transported to the Texas Tech University Beef Center in New Deal, TX. Cattle were weighed and scanned using real-time ultrasound. Resulting data were used to predict empty body fat percentage (pEBF %). Steers (n=48; BW = 520 ± 30.4 kg; pEBF % = 26.2 ± 1.9) and heifers (n=48; BW = 466 ± 29.5 kg; pEBF % = 26.7 ± 1.7) were blocked within gender by pEBF % in a completely randomized block design and randomly assigned to pen (2 pens/block; 4 hd/pen) and treatment (6 pens/treatment): 1) control heifers (HC), 2) ZH heifers (HZ), 3) control steers (SC), 4) ZH steers (SZ). Movement differences were objectively assessed on day 0, 5, 10, 15 and 20 with several measures of mobility: exit velocity from chute (EV), velocity traveling from the pen to chute (VT) and velocity traveling from chute to pen (VF). Chute scores (CS) were assigned to all cattle based on a scale ranging from 1 to 5 (1 = no distress, 5 = high distress). Prior to shipping, individual locomotion scores (LS) were recorded based on a 1 to 4 scale (1 = no lameness, 4 = severe lameness). No significant gender x treatment interactions were found for any measured variable (P ≥ 0.46). A significant treatment x day interaction (P = 0.03) was detected for EV, indicating that ZH cattle became progressively slower throughout the treatment period. No significant effects were found for VT or VF (P ≥ 0.31). Fisher’s exact test for count data was used to analyze the frequency distributions for both subjective measures. On d 20, a greater proportion (P = 0.01) of ZH cattle exhibited elevated chute scores (CS ≥ 3) relative to control. There was a tendency (P = 0.09) for increased locomotion score (LS ≥ 2) in ZH fed cattle. However, the proportion of cattle with locomotion scores indicating sufficiently sound movement (LS = 1&2) versus cattle that were moderate or severely lame (LS = 3&4) was not significantly different between treatment groups (P = 0.24). These data suggest that ZH supplementation may slightly limit mobility of cattle; nonetheless, the magnitude of these effects is not sufficient to deduce a detriment to cattle soundness.
Keywords: cattle, zilpaterol hydrochloride, mobility