The anesthetic and cardio-respiratory effects of xylazine-alfaxalone combination
were evaluated in calves. Six calves (age: 6–9 months old; weight: 114–310 kg) were anesthetized
with intravenous alfaxalone 15 min after administration of intramuscular saline (0.5 ml/100 kg)
or xylazine (0.1 mg/kg; 0.5 ml/100 kg of a 2% xylazine solution). Anesthesia induction was
smooth and orotracheal intubation was achieved in all calves. The calves anesthetized with
xylazine-alfaxalone required a smaller induction dose of alfaxalone (1.23 ± 0.17 mg/kg, P=0.010)
and accepted endotracheal intubation for a significantly longer period (16.8 ± 7.2 min, P=0.022)
than the calves anesthetized with alfaxalone alone (2.28 ± 0.65 mg/kg 7.3 ± 1.6 min). At 5 min
after induction, tachycardia (heart rate: 166 ± 47 beats/min of heart rate), hypertension (mean
arterial blood pressure: 147 ± 81 mmHg), and hypoxemia (partial pressure of arterial blood
oxygen [PaO2]: 43 ± 10 mmHg) were observed in the calves anesthetized with alfaxalone alone,
whereas hypoxemia (PaO2: 47 ± 7 mmHg) and mild hypercapnia (partial pressure of arterial blood
carbon dioxide: 54 ± 5 mmHg) were observed in the calves anesthetized with xylazine-alfaxalone.
Premedication with xylazine provided a sparing effect on the induction dose of alfaxalone and
a prolongation of anesthetic effect. Oxygen supplementation should be considered to prevent
hypoxemia during anesthesia.