Evaluation of a new anaesthetic protocol in ring-tailed lemurs (Lemur catta)

Lemur catta are endangered prosimians often kept in zoological exhibits. Chemical immobilization is most of the time compulsory to perform veterinary procedures in these animals [1]. The aim of this observational study is to evaluate the quality of sedation, induction and maintenance of anaesthesia and cardiorespiratory effects of a new anaesthetic protocol in ring-tailed lemurs undergoing bilateral orchiectomy. The study was carried out at Valcorba Zoological Park (Pozzonovo, PD, Italy) following internal ethical clearance approval. Six healthy adult ring-tailed lemurs were sedated with a combination of dexmedetomidine (0.015 mg/kg), midazolam (0.2 mg/kg) and butorphanol (0.2 mg/kg) administered intramuscularly. To perform oral intubation, alfaxalone (0.5 mg/kg) was administered intravenously over 60-seconds and further boluses of 0.2 mg/kg were given every 20 seconds if needed. The inital infusion rate of alfaxalone (0.1 mg/kg/minute) was adjusted to maintain cardiovascular and respiratory stability while performing the surgical procedure. Heart rate, ECG, SpO2, rectal temperature, respiratory rate, EtCO2 and non-invasive blood pressure were recorded every 5 minutes throughout surgery and recovery. Quality of sedation, induction, manteinance and recovery were assessed, and reaction to manipulation scored. These assessments were performed by the same observer using a descriptive scoring system specifically designed for this study. Quantitative data were analysed with two-way Anova and the Bonferroni correction using SAS statistical software (version 9.3, SAS Institute). P values < 0.05 were deemed significant. Sedation at 20 minutes was scored as “profound” in alll animals and no reactions to manipulation were seen. Induction and intubation were scored as “smooth and uneventful” in all animals but one, which was scored as “satisfactory”. Three out of six animals had self-limiting muscle twitching at induction. Maintenance of anaesthesia was scored as “good” in five animals. Only one speciment showed respiratory depression, thus oxygen was administered and ventilatation manually assisted. Heart rate and respiratory rate decreased 15 min after the beginning of alfaxalone infusion (p<0.05). Alfaxalone infusion was discontinued at the end of the surgery and, although extubation was possible after 15.33 ± 8.02 min, atipamezole had to be administered to achieve full recovery after 38 ± 5 minutes from injection. In conclusion, the combination of drugs proposed in this study offered a reliable sedation and anaesthesia in lemurs, nevertheless careful monitoring is always recommended.