Cardiorespiratory and metabolic effects of xylazine, detomidine, and a combination of xylazine and acepromazine administered after exercise in horses

Objective-To determine sedative, cardiorespiratory and metabolic effects of xylazine hydrochloride, detomidine hydrochloride, and a combination of xyl azine and acepromazine administered IV at twice the standard doses in Thoro ughbred horses recuperating from a brief period of maximal exercise. Animals-6 adult Thoroughbreds. Procedure-Horses were preconditioned by exercising them on a treadmill to e stablish a uniform level of fitness. Each horse ran 4 simulated races, with a minimum of 14 days between races. Simulated races were run at a treadmil l speed that caused horses to exercise at 120% of their maximal oxygen cons umption. Horses ran until they were fatigued or for a maximum of 2 minutes. One minute after the end of exercise, horses were treated IV with xylazine (2.2 mg/kg of body weight), detomidine (0.04 mg/kg), a combination of xyla zine (2.2 mg/kg) and acepromazine (0.04 mg/kg), or saline (0.9% NaCl) solut ion. Treatments were randomized so that each horse received each treatment once, in random order. Cardiopulmonary indices were measured, and samples o f arterial and venous blood were collected immediately before and at specif ic times for 90 minutes after the end of each race. Results-All sedatives produced effective sedation. The cardiopulmonary depr ession that was induced was qualitatively similar to that induced by admini stration of these sedatives to resting horses and was not severe: Sedative administration after exercise prolonged the exercise-induced increase in bo dy temperature. Conclusions and Clinical Relevance-Administration of xylazine, detomidine, or a combination of xylazine-acepromazine at twice the standard doses produ ced safe and effective sedation in horses that had just undergone a brief, intense bout of exercise.