| Summary: | Doctor of Philosophy === Department of Diagnostic Medicine/Pathobiology === Daniel U. Thomson === Beta-adrenergic agonists (βAA) are administered during the final weeks of the beef production system to improve efficiency and increase meat yield. Welfare concerns linked to the administration of βAA have garnered significant attention in recent years due to anecdotal reports of increased mortality during βAA feeding periods and cattle without obvious disease or injury having difficulty walking at abattoirs being overrepresented in cattle fed βAA. Thomson et al. (2015) reported 2 events where cattle were distressed, became non-responsive to handling, sloughed hoof walls and were euthanized while in lairage at the abattoir. Consistent blood abnormalities in euthanized cattle included elevated blood lactate (25.6 mmol/L; ref. range: < 4-5) and creatine kinase (CK; 6,890 U/L, ref. range: 159- 332). Although no causal relationship had been established, dialogues among groups of packers, animal scientists, and welfare experts implicating the βAA zilpaterol hydrochloride (ZIL; Zilmax®, Merck Animal Health, Desoto, KS) as one possible etiology resulted in a major beef packer announcing plans to stop accepting cattle fed ZIL. Consequently, Merck announced a self-imposed suspension of ZIL sales in U.S. and Canadian markets until further research could be conducted to investigate the manner. Utilization of technologies such as βAA are imperative to meeting the demands of a growing world population and verdicts regarding such technologies, including their impact on animal welfare, should be based on scientific merit. The first objective of this research was to evaluate the effect of shade on performance and animal well-being in cattle fed ZIL. The second objective was to characterize the clinical description and hematological profile of fatigued cattle presented to abattoirs. The third objective was to evaluate the effects of handling intensity during shipment for slaughter in cattle fed a βAA. The fourth objective was to evaluate the effects of βAA administration on performance and physiological response to different handling intensities
during shipping for slaughter. Shade provision reduced open-mouth breathing and increased dry matter intake and dressing percentage. Fatigued cattle observed at abattoirs had increased respiratory rates and muscle tremors, although blood parameters were relatively normal compared to their cohorts. Metabolic acidosis, a precursor for Fatigued Cattle Syndrome, was observed in cattle exposed to aggressive handling regardless of βAA status. This research confirms the improved growth performance of cattle fed βAA and highlights the improvement of animal welfare through shade provision and low-stress handling in heavy-weight feedlot cattle.
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