A study was performed to assess the effect of
xylazine HCl (0.1 mg/kg of
body weight, IV) in heifers maintained at thermoneutrality (18 C, 42% humidity) or under heat stress (33 C, 63% humidity) conditions.
Xylazine caused 50 and 70% decreases in serum
insulin concentrations in the thermoneutral and heat-stressed heifers, respectively.
Xylazine-induced hypoinsulinemia was associated with
hyperglycemia. In the thermoneutral group, serum
glucose concentrations increased from a basal concentration of 75 mg/dl to 150 mg/dl after 15 minutes. In the heat stress group, the serum
glucose concentration increased from 65 mg/dl to 105 mg/dl.
Hyperglycemia peaked at 2 hours and remained high for 6 hours after
xylazine administration. Heat-stressed heifers took a longer time (107 minutes) to stand than did heifers under thermoneutral conditions (41 minutes). The time to regain sensation to
pain was significantly prolonged in heat-stressed heifers.
Xylazine had no effect on body temperature and respiration rate in heifers under the thermoneutral condition, whereas it markedly
induced hyperthermia and suppressed respiration rate in the heat-stressed heifers. Furthermore, the pulse rate was slightly decreased in thermoneutral heifers and was markedly decreased in the heat-stressed heifers.