Combined xylazine and ketamine as an analgesic regimen in sheep

OBJECTIVE: To determine whether low dose xylazine with ketamine reduces the concentrations of cortisol and prolactin in sheep postoperatively and to characterise the effects of the drugs on behaviour during recovery. DESIGN: Analysis of variance was used to compare the effects of anaesthesia, surgery and combined ketamine/xylazine treatment on the plasma cortisol and prolactin concentrations and on behavioural variables in pregnant ewes subjected to abdominal surgery. PROCEDURE: Twelve ewes were randomly assigned to receive either ketamine/xylazine or placebo in association with anaesthesia and surgery. Both groups of ewes underwent anaesthesia alone followed a week later by anaesthesia with laparotomy and hysterotomy. Plasma cortisol and prolactin concentrations were assayed during these procedures and for 5 days afterwards. Behavioural observations were made remotely during recovery from anaesthesia and anaesthesia plus surgery. RESULTS: The concentrations of cortisol in the plasma of pregnant ewes undergoing surgery were increased by preoperative handling and the onset of thiopentone/halothane anaesthesia, with a further increase during surgery (P = 0.033). Cortisol concentrations decreased over the first four postoperative hours (P = 0.029) and were normal by 24 h. The drug treatment did not affect the immediate responses of ewes to anaesthesia or surgery, although treated ewes had lower cortisol concentrations than saline-treated controls over the first five postoperative days (P = 0.018). Prolactin concentrations increased in response to anaesthesia (P = 0.047), but were not affected by surgery or the drug treatment. Drug-treated ewes had prolonged sleeping time after surgery (P = 0.002), but they took no longer to stand than saline-treated controls and required fewer attempts to stand successfully (P = 0.025). CONCLUSION: At the doses used, ketamine and xylazine did not mitigate the immediate endocrine consequences of surgery but the behavioural data provide a basis for further investigations that may lead to improvements in analgesic treatments.