The hairy lizard: heterothermia affects anaesthetic requirements in the Arabian oryx (Oryx leucoryx).

Objective To study the effect of heterothermia on anaesthetic drug requirements in semi-free ranging Arabian oryx and to assess the temperature quotient (Q10) of oxygen consumption. Study design Prospective observational study and controlled metabolic experiment. Animals Sixty-eight anaesthetic events in 59 Arabian oryx fromMahazat As-Sayd protected area, Saudi Arabia. Methods Anaesthesia was induced by remote injection of 25 mg ketamine, 10 mg midazolam and 0.5 mg medetomidine with a variable amount of etorphine based on a target dosage of 20 µg kg-1 and subjective assessment of body mass. Animals not recumbent within 15minutes or insufficiently anaesthetized were physically restrained and administered supplementary etorphine intravenously depending on the anaesthetic depth. Body temperature (Tb) was measured rectally immediately upon handling of each animal. Fromsix anaesthetized oryx, expiratory gasses for oxygen analysis and metabolic rate calculation were collected at twoTbs; before and after submersion in icewater for approximately 30 minutes. Results: Forty-two animals (62%) became recumbent with the initial dose, with a mean induction time (± standard deviation) of 9 ± 2 minutes. The remaining animals could be handled but needed 0.3 ± 0.1 mg etorphine intravenously to reach the desired level of anaesthesia. There was a significant positive correlation between Tb and effective etorphine dosage (R² = 0.48, p < 0.0001). Average Tb of the six animals in which metabolic rate was measured decreased from 40.0 ± 0.5°C immediately after induction to 35.5 ± 0.5°C after cooling. This reduction was associated with a reduction in oxygen uptake from 3.11 ± 0.33 to 2.22 ± 0.29 mL O2 minute-1 kg-1, reflected in Q10 of 2.17 ± 0.14. Conclusions and clinical relevance: Tb significantly affects anaesthetic requirements in Arabian oryx and should be considered when selecting dosages for anaesthetic induction for species showing diurnal heterothermy. [ABSTRACT FROM AUTHOR]