The effects of zilpaterol hydrochloride and shade on blood metabolites of finishing beef steers

The effects of feeding zilpaterol hydrochloride (ZH) and shade were evaluated on blood metabolites in finishing beef steers (n = 480). Cattle were fed 0 or 8.33 mg/kg of diet DM ZH for 21 d with a 3- or 4-d withdrawal before harvest and were housed in open or shaded pens. Blood samples were collected the day before ZH was fed and on the day the cattle were shipped to the commercial abattoir. Lactate concentration was not different between cattle fed ZH in open or shaded pens (P = 0.12). Nonetheless, a tendency for a diet × time interaction was detected for lactate concentration (P = 0.09), in which it was greater in cattle fed the control diet in open pens before and after ZH was fed (P = 0.01). Glucose was greater for cattle fed the control diet than cattle fed ZH for 21 d (P = 0.03). Cattle fed in open vs. shaded pens did not differ in glucose concentration (P = 0.12), whereas glucose concentrations were greater before ZH was fed than after (P = 0.02). In contrast, plasma urea nitrogen (PUN) concentration was not different in response to diet (P = 0.24), housing type (P = 0.65), or before vs. after being fed ZH (P = 0.60). Lactate concentrations were not different across diet or shade treatments before ZH was fed, whereas after ZH, lactate concentrations were greater in control cattle than cattle fed ZH. Additionally, cortisol was less after feeding ZH. Glucose was greater before than after feeding ZH.