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Comparison of ketamine and alfaxalone for induction and maintenance of anaesthesia in ponies undergoing castration


Heide Klöppel, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU, UK. E-mail:


Objective  To compare alfaxalone with ketamine for total intravenous anaesthesia in ponies undergoing castration.

Study design  Prospective, randomised, blinded clinical study.

Animals  Forty-two, 12-month-old Welsh Mountain ponies.

Methods  Ponies were assigned randomly to receive ketamine or alfaxalone. After administration of romifidine 100 μg kg−1 and butorphanol 50 μg kg−1 intravenously (IV), sedation and response to tactile stimulation were scored. If sedation was insufficient, romifidine 30 μg kg−1 was administered IV. Anaesthesia was induced with ketamine 2.2 mg kg−1 or alfaxalone 1 mg kg−1, both in combination with diazepam 20 μg kg−1 IV. Time from end of injection to lateral recumbency was recorded. Simple descriptive scores were used to score quality of induction, surgical conditions and recovery. Ketamine 0.5 mg kg−1 or alfaxalone 0.2 mg kg−1 were administered if movement was observed. Times to first head lift, sternal recumbency and standing, and number of attempts needed were recorded. All scores were performed by the same observer, unaware of treatment. Normally distributed data were compared using t-test and non-normally distributed data with Mann–Whitney test. Level of significance was set at p < 0.05.

Results  Three ponies needed additional sedation. Mean induction times were 30 ± 6 and 18 ± 4 seconds following ketamine and alfaxalone respectively (p < 0.0001). Additional doses were required by four ponies given ketamine and seven given alfaxalone. Sedation, induction and surgical scores were similar for both groups. Recovery scores (scale of 1–4 with 1 best) differed statistically between groups [ketamine group, median 1 (1–2); alfaxalone group 1.5 (1–4) (p = 0.04)]. No differences in anaesthesia time or times taken from end of surgery to head lift, sternal recumbency and standing were detected.

Conclusion and clinical relevance  Induction times following alfaxalone were shorter than following ketamine. Both anaesthetic agents provided acceptable quality of anaesthesia for castration.