HEMODYNAMIC-EFFECTS OF XYLAZINE IN THE CALF

Abstract

Whether myocardial depression was associated with the effects of this drug in intact, unanesthetized cattle was investigated. The hemodynamic effects of sedative level doses of xylazine in 5 chronically instrumented calves were studied. These effects included immediate and prolonged reductions in heart rate, cardiac output, arterial blood pressure and left ventricular dp/dt [change in pressure with time] max. Stroke volume showed an initial decrease in value with a return in 15 min to base-line values. Total peripheral resistance, end-diastolic left ventricular pressure, end-diastolic left ventricular volume and left ventricular residual fraction were increased after drug administration. A depressed myocardium evidently results from xylazine administration. With 1 exception (the absence of a hypertensive response), the effects largely parallel, both quantitatively and qualitatively, those seen with this drug on other species. Xylazine sedation is produced in cattle at doses which are small compared to that which is required for sedation in other species. These same small doses in cattle also cause hemodynamic changes.