A comparison of two ketamine doses for field anaesthesia in horses undergoing castration.

BACKGROUND: Ketamine at 2.2 mg/kg given i.v. is often used to induce anaesthesia for surgical procedures in horses under field conditions. Commonly, additional doses are needed to complete the surgery. We hypothesised that surgical conditions would be improved when 5 mg/kg of ketamine was used to induce anaesthesia, while induction and recovery qualities would not differ from those when 2.2 mg/kg ketamine was used.

OBJECTIVE: To compare the anaesthetic effects of two ketamine doses (5 mg/kg and 2.2 mg/kg) during field anaesthesia for castration of horses.

STUDY DESIGN: Prospective, randomised, blinded, clinical study.

METHOD: Seventy-seven client-owned Icelandic horses presenting for castration under field conditions were studied. Pre-anaesthetic medication was xylazine (0.7 mg/kg) butorphanol (25 μg/kg) and acepromazine (50 μg/kg) injected i.v. Anaesthesia was induced with either 2.2 mg/kg (K2.2) or 5 mg/kg (K5) i.v. of ketamine mixed with diazepam (30 μg/kg). The quality of induction, surgical conditions and recovery were compared using subjective and objective measures, and the number of additional ketamine doses recorded.

RESULTS: Ketamine 5 mg/kg provided better surgical conditions and a more rapid induction. Recovery quality was subjectively better in K2.2. Five horses in K2.2 and two in K5 required additional ketamine doses.

MAIN LIMITATIONS: While the pre-anaesthetic sedation and benzodiazepine doses were consistent among horses, the level of sedation and muscle relaxation achieved before induction differed.

CONCLUSION: A ketamine dose of 5 mg/kg can be used to improve the quality of field anaesthesia for castration in Icelandic horses. Although recovery quality is subjectively poorer with this dose, no adverse events were observed during recovery. This article is protected by copyright. All rights reserved.