EFFECT OF XYLAZINE ON SOME ENDOCRINOLOGICAL AND HAEMATOLOGICAL PARAMETERS IN HEIFERS UNDER THERMONEUTRAL OR HEAT STRESS CONDITIONS

Abstract

A study was performed to assess the effect of xylazine HCI (0.1 mg/kg of body weight, IV) in heifers maintained at thermoneutral (TN; 18°C, 42% RH) or heat stress (HS;33°C, 63% RH) conditions. Xylazine injection resulted in a sharp increase (P<0.05) in serum cortisol levels after 15 minutes in both groups. However, cortisol levels gradually declined and reached basal levels after 45 minutes and 3 hours in heifers maintained under TN and HS conditions, respectively. Xylazine administration increased (P<0.05) serum T3 concentrations after 15 and 30 minutes in the thermoneutral and heat-stressed animals, respectively. Serum T3, however, gradually decreased and reached basal values after 3 hours in both groups. The xylazine-treated heifers had lower (P<0.05) red blood cells, haemoglobin and packed cell volume under TN conditions, while higher (P<0,05) values were observed under HS conditions. All the above parameters were greater (P< 0.05) in the thermoneutral animals than in the heat-stressed ones either before or after xylazine administration. It is possible that an undesirable interaction occurred between xylazine and the hot environment, thus it is suggested that xylazine should be used cautiously in hyperthermic animals.