Effects of zaliapaterol hydrochloride on mobility, general animal wellbeing and the thermoregulatory response of feedlot steers and heifers during moderate stress heat
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The objectives of this study were to determine the effects of zilpaterol hydrochloride (ZH) feeding on cattle well-being by evaluating: 1) mobility and chute temperament 2) various indicators of physiological/metabolic stress and 3) post-mortem histopathology. Steers and heifers (n=96) were sourced from a commercial feedlot and transported to the Texas Tech University Beef Center. 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 complete randomized block design and randomly assigned to pen (2 pens/block; 4 hd/pen) and treatment (6 pens/treatment). Movement differences were objectively assessed (d 0, 5, 10, 15 and 20) with several measures of mobility: exit velocity from chute (EV), velocity traveling to the working area (VT) and velocity returning to the home pen (VF). Individual locomotion scores (LS) were recorded based on a 1 to 4 scale (1 = no lameness, 4 = severe lameness). Venous blood was collected via jugular venipuncture (d 0, 5, 10, 15 and 20) and analyzed for various markers of physiological/metabolic stress. Skeletal muscle and cardiac tissue were evaluated for gene expression of creatine phosphokinase (CPK) using PCR. Cattle fed ZH displayed a TRT*TIME interaction for EV (P = 0.03) driven by an increase at d 5 (P = 0.03). Pooled treatment effects were not significant for VT or VF (P ≥ 0.31). 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 different between treatment groups (P = 0.24). Blood potassium concentration increased with ZH treatment (P < 0.01). A TRT*SEX interaction was detected for blood ionized calcium (P = 0.03) indicating a ZH related reduction in both genders, but the magnitude of the effect was greater in steers. The concentration of serum NEFA was increased in ZH treated cattle (P = 0.03). Treatment effects were not detected for CPK in serum (P = 0.70) or local tissue (P > 0.13). No treatment effects were detected in the histopathology analysis (P > 0.50). Collectively, these data suggest that ZH supplementation does not impair cattle soundness of movement or apparent well-being; however, notable changes occur in terms of metabolic parameters in the blood.