The Hairy Lizard: Factoring in Heterothermy in Anesthetic Management of Arabian Oryx (Oryx leucoryx)
American Association of Zoo Veterinarians Conference 2015
Mads F. Bertelsen1, DVM, DVSc, DACZM, DECZM (Zoo Health Management); Osama Mohammed2, BVM, MVSc, PhD; Tobias Wang3, MSc, PhD; Paul Manger4, MSc, PhD; Michael Scantlebury5, MA, PhD; Khairi Ismael6, MSc; Abdulaziz Alagaili2, MSc, PhD
1Copenhagen Zoo, Centre for Zoo and Wild Animal Health, Frederiksberg, Denmark; 2Zoology Department, King Saud University, Riyadh, Saudi Arabia; 3Department of Zoophysiology, Aarhus University, Denmark; 4School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, Republic of South Africa; 5School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, Northern Ireland; 6National Wildlife Research Center, Taif, Saudi Arabia; 7Saudi Wildlife Authority, Riyadh, Saudi Arabia
Abstract
The core body temperature (Tb) of mammals is generally expected to be constant and is usually not factored in when selecting anesthetic dosages. However, several mammals show heterothermy to save energy and water. For example, the daily Tb of the Arabian oryx (Oryx leucoryx) fluctuates by as much as 5°C.1,2 Such variation in Tb might affect metabolic rate and thus anesthesia. We investigated the effect of Tb on the anesthetic dosage required in 68 anesthetic events of semi-free ranging Arabian oryx. Anesthesia was induced by remote injection of a set amount of ketamine (25 mg), midazolam (10 mg), and medetomidine (0.5 mg) combined with a variable amount of etorphine (target dosage: 20 µg/kg). If an animal did not become recumbent within 15 min after darting, or was insufficiently anesthetized, it was given a supplementary injection of etorphine (0.2–0.4 mg IV) depending on anesthetic depth. The Tb was measured immediately upon handling of the animal. Forty-two animals (62%) became recumbent following the initial dose. The remaining animals could be handled but needed 0.3±0.14 mg etorphine IV to reach the desired level of anesthesia. There was a significant positive correlation between Tb and the total etorphine dosage needed (r2=0.4677, p<0.0001); at low Tb (<37°C), as little as 16–20 µg/kg was sufficient, whereas above 41°C twice that amount was required. In eight animals, basic metabolic rate was assessed based on oxygen consumption at two different Tbs: a 30–40% reduction in oxygen uptake with a decrease in Tb of 4–5°C was demonstrated, supporting the notion that Tb must be considered when anesthetizing heterothermic animals.
Literature Cited
1. Hetem RS, Strauss WM, Fick LG, et al. Variation in the daily rhythm of body temperature of free-living Arabian oryx (Oryx leucoryx): does water limitation drive heterothermy? J Comp Physiol B. 2010;180:1111–1119.
2. Ostrowski S, Williams JB, Ismael K. Heterothermy and the water economy of free-living Arabian oryx (Oryx leucoryx). J Exp Biol. 2003;206:1471–1478.