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.
Highlights
In the United States, two β-adrenergic agonists are approved for the purpose of growth promotion in cattle fed in confinement for slaughter: ractopamine hydrochloride[1], a predominantly β1AA, and zilpaterol hydrochloride[2], a predominantly β2AA
The mass of the left ventricle tended to be positively associated with diastolic Pulmonary arterial pressure (PAP) in zilpaterol treated steers (ZS), but there was no association between left ventricular mass and diastolic PAP in Control steers (CS)
The findings of this study indicate that, in the feedlot studied, the β2AA zilpaterol hydrochloride is associated with left ventricular hypertrophy and myocardial injury
Summary
In the United States, two β-adrenergic agonists (βAA) are approved for the purpose of growth promotion in cattle fed in confinement for slaughter: ractopamine hydrochloride[1], a predominantly β1AA, and zilpaterol hydrochloride[2], a predominantly β2AA. A large observational study concluded that 40 to 50% of deaths among feedlot cattle treated with the β2 adrenergic receptor-selective agonist zilpaterol hydrochloride (Zilmax®, Merck Animal Health, Summit, NJ, USA) were attributable to the drug[9] The etiology of this increased mortality risk has not been investigated, but anecdotal reports suggest that cattle fed β2AA are at increased risk of heart failure. 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. Conclusions: Our findings suggest that zilpaterol hydrochloride induced sufficient left ventricular hypertrophy to cause impaired left
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