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 xylazine and acepromazine administered i.v. at twice the standard doses in Thoroughbred horses recuperating from a brief period of maximal exercise.


METHODS
6 adult Thoroughbreds.


METHODS
Horses were preconditioned by exercising them on a treadmill to establish 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 treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until they were fatigued or for a maximum of 2 minutes. One minute after the end of exercise, horses were treated i.v. with xylazine (2.2 mg/kg of body weight), detomidine (0.04 mg/kg), a combination of xylazine (2.2 mg/kg) and acepromazine (0.04 mg/kg), or saline (0.9% NaCl) solution. Treatments were randomized so that each horse received each treatment once, in random order. Cardiopulmonary indices were measured, and samples of arterial and venous blood were collected immediately before and at specific times for 90 minutes after the end of each race.


RESULTS
All sedatives produced effective sedation. The cardiopulmonary depression that was induced was qualitatively similar to that induced by administration of these sedatives to resting horses and was not severe. Sedative administration after exercise prolonged the exercise-induced increase in body temperature.


CONCLUSIONS
Administration of xylazine, detomidine, or a combination of xylazine-acepromazine at twice the standard doses produced safe and effective sedation in horses that had just undergone a brief, intense bout of exercise.
Hubbell
J A
JA
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus 43210, USA.
Hinchcliff
K W
KW
Schmall
L M
LM
Muir
W W
WW
Robertson
J T
JT
Sams
R A
RA
D000075:Acepromazine / Q000494:pharmacology*; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000187:drug effects; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006736:Horses; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects*; D010805:Physical Conditioning, Animal; D005082:Physical Exertion / Q000502:physiology*; D011651:Pulmonary Artery / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects; D014991:Xylazine / Q000494:pharmacology*
D000700:Analgesics; D006993:Hypnotics and Sedatives; D007093:Imidazoles; D002245:Carbon Dioxide; D014991:Xylazine; D000075:Acepromazine; C041255:detomidine; D010100:Oxygen