Evaluation of the Effects of Isoflurane Anaesthesia on Gastrointestinal Transit Time, Feed Intake and Defecation in Rabbits

BACKGROUND: Domestic rabbits are popular companion animals, resulting in a growing demand for veterinary procedures requiring anaesthesia. However, due to their unique characteristics, anaesthetizing rabbits is challenging and carries a high risk of peri-anaesthetic mortality and gastrointestinal (GI) complications. Isoflurane is a commonly used inhalation anaesthetic, but no studies have assessed its potential effects on GI transit time in rabbits. OBJECTIVES: The present study aims to assess whether varying durations of isoflurane anaesthesia affect GI transit time, feed intake and defecation in healthy rabbits. METHODS: Five healthy adult male New Zealand White rabbits participated in a repeated measures study comprising four conditions: (1) awake (control), (2) 15 min, (3) 30 min and (4) 60 min of anaesthesia with isoflurane, each separated by a 6-day washout period. Anaesthesia was induced with 5% isoflurane in 100% oxygen using an induction chamber and maintained with 1.5%-3% isoflurane in oxygen delivered via an endotracheal tube to achieve deep surgical anaesthesia. GI transit time was evaluated via barium sulphate contrast radiography at 1, 15, 30, 60, 120, 240, 360 and 420 min post-administration. The study assessed three transit markers: (1) gastric transit time, (2) small intestinal transit time and (3) time to hard faeces formation. Feed intake and faecal output were also recorded daily for 6 days after each anaesthetic condition. RESULTS: (3) = 10.41, p = 0.015, Kendall's W = 0.69); however, pairwise comparisons between anaesthesia conditions and the awake control were not statistically significant. The 60-min group had the highest median transit time (120 min), compared with 60 min in the other three conditions. No significant differences were observed in time to hard faeces formation among conditions (p = 0.152). Feed intake and faecal output did not differ across anaesthetic durations (p > 0.05 for all comparisons). CONCLUSIONS: Under the experimental conditions studied, isoflurane anaesthesia was not associated with significant changes in gastric transit, the time to hard faeces formation, feed intake or faecal output in healthy male rabbits. Although we observed an overall difference in small intestinal transit time, no anaesthetic group showed a statistically significant variation from the awake control phase. Furthermore, the discrete nature of radiographic assessments and the small sample size limit definitive conclusions regarding a clinically relevant isoflurane-induced transit delay. Further studies with larger sample sizes and more precise transit-time measurement techniques are recommended.