Comparison of anaesthetic and cardiorespiratory effects of xylazine or medetomidine in combination with tiletamine/zolazepam in pigs

Two different combinations of anaesthetics were evaluated and compared in a prospective randomised crossover experimental study in pigs. One of the two combinations was administered intramuscularly to each of six Landrace x Yorkshire mixed-breed pigs. The combinations were: 2.2 mg/kg xylazine and 4.4 mg/kg tiletamine/zolazepam (2.2 mg/kg tiletamine plus 2.2 mg/kg zolazepam) (XTZ); and 0.04 mg/kg medetomidine and 4.4 mg/kg tiletamine/zolazepam (MTZ). The anaesthesia and recovery times, score for anaesthetic effect and cardiopulmonary parameters were recorded for each pig. Anaesthesia was successfully induced in all of the pigs. Both drug combinations provided smooth induction and good immobilisation, and their anaesthetic effects were similar. In both treatment groups, the mean heart rate decreased significantly five minutes after the drugs were administered and remained consistent for 70 minutes, with no significant difference between the XTZ and MTZ groups. However, there were differences in cardiopulmonary effects between the groups. The arterial pressure was significantly higher in the MTZ group than in the XTZ group. The initial hypertension associated with medetomidine was more marked than the initial hypertension associated with xylazine. Arterial oxygen partial pressure and arterial oxygen saturation decreased significantly from baseline in both groups. The respiratory rates and levels of blood gases were similar in both groups. Hypoventilation and hypoxaemia were observed in both groups. The scores for anaesthetic effect, induction time, anaesthesia time and recovery times were similar in the two groups.