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

Authors: Hales Paxton, Kristin; Foote, Andrew; Jones, Shuna; Shackelford, Steven; BOYD, BRADLEY - University Of Nebraska; ERICKSON, GALEN - University Of Nebraska

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2016
Publication Date: 8/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63035
Citation: Hales Paxton, K.E., Foote, A.P., Jones, S., Shackelford, S.D., Boyd, B.M., Erickson, G.E. 2016. The effects of zilpaterol hydrochloride and shade on blood metabolites of finishing beef steers. Journal of Animal Science. 94(7):2937-2941. doi:10.2527/jas2015-9967.

Interpretive Summary: The effects of feeding zilpaterol hydrochloride and shade were evaluated on blood metabolites and lung score in finishing beef steers. Cattle were fed a control or zilpaterol hydrochloride diet for 21 days with a 3- or 4-day withdrawal before harvest and were housed in open or shaded pens. Blood samples and lung scores were collected the day before zilpaterol hydrochloride was fed and on the day the cattle were shipped for harvest. Blood lactate concentration was not different between zilpaterol hydrochloride and control fed cattle fed in open or shaded pens. Cortisol, a measure of acute stress, was less in cattle after they had been fed zilpaterol hydrochloride. Blood glucose levels were greater for cattle fed the control diet than fed zilpaterol hydrochloride for 21 days. Plasma urea nitrogen was not different across any treatments. Lung scores measured using a digital stethoscope were increased (worse) after zilpaterol hydrochloride was fed. From these data we interpret that metabolic profiles change in response to feeding zilpaterol hydrochloride. Cattle fed zilpaterol hydrochloride are less glucose dependent and likely more dependent on fatty acid breakdown. The lack of differences in cortisol and lactate concentrations indicate that there was not an acute stress response associated with cattle fed control or zilpaterol hydrochloride diets in shade or open pens.

Technical Abstract: The effects of feeding zilpaterol hydrochloride (ZH) and shade were evaluated on blood metabolites and lung score in finishing beef steers. Cattle were fed 0 or 8.33 mg/kg ZH for 21 d with a 3- or 4-d withdrawal before harvest and were housed in open or shaded pens. Blood samples and lung scores 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 being fed ZH. Cortisol concentration was different before and after ZH was fed (P = 0.01) in that it was less after ZH was fed. 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). The lung score was greater for cattle fed the control diet vs. the ZH diet (P = 0.03), and greater for cattle fed in open pens vs. shaded pens (P = 0.02). Additionally, the lung scores tended to be greater after ZH was fed than before (P = 0.10). The change in lactate was not different in response to the diet (P = 0.46) or the type of housing used (P = 0.24) from before the cattle were fed ZH to after. Additionally, the change in cortisol, glucose, lactate, PUN, and lung score was not different because of diet (P > 0.58) or housing (P > 0.22). The analysis of change in metabolite concentrations over time revealed no differences; however, there were less degrees of freedom associated with this analysis. 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 in control than ZH fed cattle, and glucose was greater before than after feeding ZH.