Abstract
The anesthetic and cardiorespiratory 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 m
l
/100 kg) or xylazine (0.1 mg/kg; 0.5
m
l
/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
[PaO
2
]: 43 ± 10 mmHg) were observed in the calves anesthetized with
alfaxalone alone, whereas hypoxemia (PaO
2
: 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.