Assessment of arterial oxygenation and acid-base status before and during oxygen therapy in captive European bison (Bison bonasus) immobilized with etorphine, acepromazine and xylazine
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Chemical immobilization of captive European bison (Bison bonasus) is often required for veterinary care, transport, or husbandry practices playing an important role in the reintroduction and preservation of the species. To help preventing unexpected events and reduce its negative impact we documented the efficiency and physiological effects of a combination of etorphine-acepromazine-xylazine for European bison immobilization and the benefit of oxygen therapy. Thirty-nine captive European bison were ground-darted with a combination of 1.5 mg of etorphine hydrochloride, 6.1 mg of acepromazine maleate and 20 mg xylazine hydrochloride for 100 kg of estimated weight. Arterial blood was sampled on average 20 minutes after recumbency and again 15 minutes later and immediately analyzed with a portable analyzer. At the same time heart rate, respiratory rate and rectal temperature were recorded. After the first sample we delivered oxygen intranasally at a flow rate of 1L per 100 kg of estimated weight until the end of the procedure. Before oxygen therapy the mean PaO2 was 46.7 mmHg with 32 out of 33 sampled bison presenting hypoxemia. We also observed lowered values of respiratory rate, decreased pH, and mild hypercapnia consistent with the development of a mild respiratory acidosis. Oxygen therapy allowed the resolution of hypoxemia in 22 out of 32 bison but also accentuated the respiratory acidosis. Bison immobilized with higher initial dose did not require reinjection during the procedure. Additionally, we observed that lower mean rectal temperatures during the immobilization event was significantly associated with longer recovery times. For three bison presence of ruminal fluid was noticed in the mouth and nose, causing a risk for aspiration. No mortality related to the immobilizations were reported for at least two months following the procedure. In conclusion, a combination of 0.016 mg.kg-1 etorphine hydrochloride, 0.065 mg.kg-1 acepromazine maleate and 0.22 mg.kg-1 xylazine hydrochloride provides a sufficient level of immobilization for diverse common management and husbandry procedures in captive European bison. Although, it is associated with development of marked hypoxemia, a small risk of regurgitation and mild respiratory acidosis. We recommend implementing oxygen supplementation when using this protocol.