An evaluation of chemical restraining agents in the horse.

An evaluation of acepromazine (0.5 mg/kg intramuscularly), azaperone (0.7 and 0.9 mg/kg intramuscularly) and xylazine (2.0 mg/kg intramuscularly) as chemical restraining agents was carried out in seven horses. (Xylazine and azaperone were used at the recommended dose rates; acepromazine at five times the recommended dose rates). Of the three drugs administered only azaperone produced sufficient sedation in all the horses to allow a percutaneous needle muscle biopsy to be taken from six muscles. With acepromazine and xylazine this procedure could be successfully carried out in five and four horses respectively. Both acepromazine and azaperone produced a mild transient tachycardia and a fall in packed cell volume but all three drugs reduced the "stress" of muscle biopsy as measured by increases in heart rate. Azaperone produced an increase in plasma 11-OHCS levels when administered to control animals. The measurement of changes in plasma 11-OHCS levels was not found to be a satisfactory means of assessing any reduction of "stress" with some sedative agents.