Short Communication
Effects of intracoelomic alfaxalone–dexmedetomidine on righting reflex in common garter snakes (Thamnophis sirtalis): preliminary data

https://doi.org/10.1016/j.vaa.2020.08.002Get rights and content

Abstract

Objective

To evaluate the effect of dexmedetomidine on alfaxalone immobilization in snakes.

Study design

Nonblinded, crossover study.

Animals

A total of eight mature common garter snakes (Thamnophis sirtalis).

Methods

Snakes were administered each of three treatments intracoelomically: alfaxalone (30 mg kg–1; treatment A), alfaxalone (30 mg kg–1) combined with dexmedetomidine (0.05 mg kg–1; treatment AD0.05); and alfaxalone (30 mg kg–1) combined with dexmedetomidine (0.10 mg kg–1; treatment AD0.10). A minimum of 10 days elapsed between experimental trials. Times to loss of righting reflex (LRR) and return of righting reflex (RRR) were recorded. Heart rate (HR) was recorded every 5 minutes throughout the period of LRR and averaged for each snake. Times to LRR and RRR, and mean HR in snakes that achieved LRR were reported.

Results

LRR occurred in eight (100%), five (63%) and three (38%) snakes in treatments A, AD0.05 and AD0.10, respectively. For all treatments, time to LRR ranged 3–20 minutes. Median (range) times to RRR were 39 (30–46), 89 (62–128) and 77 (30–185) minutes for treatments A, AD0.05 and AD0.10, respectively. In animals where righting reflex was lost, mean HR was lower in all dexmedetomidine treatments compared with treatment A.

Conclusions and clinical relevance

In this pilot study, alfaxalone resulted in reliable immobilization, whereas dexmedetomidine and alfaxalone combinations resulted in highly variable durations of immobilization with low HR in immobilized animals. For snakes that achieved LRR, the addition of dexmedetomidine (0.05 mg kg–1) to alfaxalone appeared to extend the period of immobilization compared with alfaxalone alone.

Introduction

Sedation or immobilization of captive and wild reptiles is often required to facilitate safe examination and to perform minor procedures. In spite of the growing need for veterinarians to become familiar with these species, there is a paucity of literature evaluating sedative and anesthetic protocols in reptiles, and very little of it pertains to snakes. Furthermore, the variables routinely used to assess anesthetic depth in mammals, including eye position, palpebral reflexes and jaw tone, are unreliable or not feasible in many reptilian species making evaluation of protocols more challenging. In snakes, the depth of anesthesia can be assessed by observing the loss of righting reflex (LRR), defined as the inability of an animal to return to a sternal position after being placed in dorsal recumbency (Scheelings et al. 2011).

Alfaxalone administered intracoelomically has recently been described as an effective means to induce LRR in the common garter snake for periods of time sufficient for short clinical procedures (Strahl-Heldreth et al. 2019). As a neurosteroid, alfaxalone exerts its anesthetic effect through γ-aminobutyric acid (GABAA) receptor modulation and is devoid of clinically significant analgesic properties in mammals (Bennell et al. 2019). Dexmedetomidine is an α2-adrenergic agonist commonly used as a sedative and muscle relaxant in reptiles and may contribute to analgesia (Sladky & Mans 2012). The antinociceptive effects of dexmedetomidine have been demonstrated in pythons suggesting that dexmedetomidine may be a valuable adjunct to injectable anesthetic protocols in snakes (Bunke et al. 2018). Additionally, the ability to antagonize dexmedetomidine facilitates a more rapid recovery in reptilian species (Doss et al. 2017). The aim of the current study was to obtain preliminary data on the effects of alfaxalone and dexmedetomidine–alfaxalone administration on LRR, time until the return of the righting reflex (RRR) and heart rate (HR) in common garter snakes. We hypothesized that the addition of dexmedetomidine would extend the period until RRR and reduce HR compared with alfaxalone administration alone.

Section snippets

Animals

A total of eight mature common garter snakes (Thamnophis sirtalis) of undetermined sex, weighing 54.7 ± 9.2 g (mean ± standard deviation), were included. Snakes were housed in individual 5 gallon glass terrariums on coconut shaving substrate with continuous access to a bowl of dechlorinated water. Environmental temperature ranged from 23 to 26 °C with humidity of 15–38%, and a 12 hour light cycle was maintained throughout the experimental period. Snakes were fed fish once weekly, and

Results

Eight (100%), five (63%) and three (38%) snakes achieved LRR in treatments A, AD0.05 and AD0.10, respectively. There were no differences between treatments A and AD0.05 (p = 0.25), A and AD0.10 (p = 0.07) or AD0.05 and AD0.10 (p = 0.48). A post hoc power analysis indicated the need for one additional snake in each treatment to reach a statistically significant difference in the proportion of snakes that achieved LRR between treatments A and AD0.10. Values for LRR, RRR and mean HR for each snake

Discussion

There was no statistically significant difference in the proportion of snakes that achieved LRR among treatments. However, there appeared to be a clinically relevant reduction in the percentage of snakes that achieved LRR with the higher dose of dexmedetomidine. This probably reflects insufficient sample size in the study as indicated by the post hoc sample size calculation, and is the result of unexpected larger variability in the dexmedetomidine treatments, compared with a priori

Conclusion

The intracoelomic administration of alfaxalone resulted in consistent immobilization in all snakes; however, the results of the study suggest that intracoelomic alfaxalone–dexmedetomidine combinations result in variable sedative effects and cannot be recommended in common garter snakes at the evaluated doses. The addition of dexmedetomidine (0.05 mg kg–1) to alfaxalone (30 mg kg–1) resulted in immobilization in five (63%) snakes with a duration that was substantially longer than that from

Acknowledgements

Funding for this study was provided in part by Zoetis, Inc.

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