The beta-adrenergic agonist zilpaterol hydrochloride may predispose feedlot cattle to cardiac remodeling and dysfunction

Abstract

Background: The aim of this study was to address producer concerns that the β2-adrenergic agonist zilpaterol hydrochloride, a bovine growth promotant, predisposes cattle to cardiac disease and death. Our objectives were to evaluate the effect of zilpaterol on cardiac function, morphology, and risk of myocardial injury. Methods: A prospective, case-control study was conducted on one feedlot in northern Colorado using convenience sampling of Angus-based steers (n = 80). Pulmonary arterial pressures (mean, systolic, and diastolic) were measured. Plasma cardiac troponin I was measured in a sub-sample of steers that were followed to slaughter (n = 31). The carcass, left ventricle plus inter-ventricular septum, and right ventricle were weighed. Results: Relative to controls, steers fed zilpaterol hydrochloride had an adjusted left ventricle and septum that was 185 g heavier (95 % CI: 19, 350 g; P = 0.03), a diastolic pulmonary arterial pressure that was 10 mm Hg greater (95 % CI: 3, 17 mm Hg; P = 0.004), and a greater concentration of cardiac troponin I (P = 0.01), a biomarker of myocardial injury. Furthermore, left ventricular mass tended to be positively and deleteriously associated with diastolic pulmonary arterial pressure in steers fed zilpaterol (P = 0.08) but not controls (P = 0.28). Conclusions: Our findings suggest that zilpaterol hydrochloride induced sufficient left ventricular hypertrophy to cause impaired left ventricular relaxation or diastolic dysfunction and myocardial injury. In conclusion, these results support concerns that, in the feedlot studied, zilpaterol hydrochloride predisposes cattle to cardiac disease.