Comparison of two ratios of xylazine:ketamine for the anesthesia of free-ranging North American beavers (Castor canadensis) in a remote setting.

The objective of this study was to evaluate and compare 2 different xylazine:ketamine combination anesthetic protocols in free-ranging beavers (Castor canadensis). Twenty-two beavers (weighing 2.5 to 18.5 kg) were equally assigned to one of the following protocols: 1:10 xylazine:ketamine ratio and 3:10 xylazine:ketamine ratio. Using standard metabolic scaling, the following ranges of dosages were calculated and used: for the 1:10 xylazine:ketamine group 1.08 to 2.25 mg/kg (median = 1.2 mg/kg) of xylazine + 10.8 to 22.5 mg/kg (median = 12 mg/kg) of ketamine IM; andfor the 3:10 xylazine:ketamine group 2.04 to 3.67 mg/kg (median = 2.7 mg/kg) of xylazine + 6.81 to 12.25 mg/kg (median = 8.8 mg/kg) ketamine IM. Measured cardiorespiratory parameters and anesthetic event intervals were compared between protocols. Both protocols rapidly induced levels of anesthesia adequate for minimally invasive procedures of short duration. Durations of immobility ranged from 15 to 35 min and were not significantly different between the protocols (P = 0.64). Recovery phases, following the IM administration of 0.2 mg/kg of atipamezole 30 to 65 min post-induction, were usually faster with the 3:10 xylazine:ketamine protocol, but this was not statistically significant (P = 0.40). Heart rates were significantly lower with the 3:10 xylazine:ketamine protocol (P = 0.0002). P_ETCO₂ values, measured with a nasal cannula, were similar between protocols and suggestive of hypoventilation. Despite the fact that the 3:10 xylazine:ketamine protocol was associated with a greater cardiac depression, the apparent, even if not statistically significant, faster recovery time with that protocol is definitively an asset for projects occurring in remote locations relying on helicopter transportation.