Welfare Implications of Low-Dose Atipamezole Reversal of Tiletamine/Zolazepam/Xylazine Anaesthesia in Pigs.

Simple Summary: Pigs are routinely used in many areas of research. Anaesthesia is commonly used in research to protect pig welfare, safely collect research samples, and achieve study objectives. Atipamezole is an anaesthetic reversal agent that is used to partially reverse the effects of anaesthesia, leading to shorter recovery times. However, anaesthetic reversal agents have also been shown to cause side effects and turbulent anaesthetic recoveries in pigs. The present study compared the recovery of anaesthetised pigs both with and without a low dose of atipamezole for the partial reversal of anaesthesia. We aimed to determine if using atipamezole reversal at a dose below the published range reduced recovery times and the physiological impacts of anaesthesia without introducing side effects and adverse behaviours. We found that while low-dose atipamezole decreased anaesthetic recovery time and improved the maintenance of core temperature in most anaesthetised pigs, it introduced and exacerbated a range of side effects and behaviours that could lead to poorer welfare outcomes for research pigs. This study provides new information on the welfare impacts of using a low dose of atipamezole for the reversal of pig anaesthesia, which will allow for the refinement of anaesthesia regimes in laboratory pigs. Anaesthesia is sometimes required for the effective restraint of laboratory pigs for sample collection. Yet, anaesthesia can initiate a range of physiological disruptions that can increase variability in study data and lead to poorer animal welfare. Judicious use of anaesthesia can mitigate experimental, human safety, and animal welfare concerns, but it does not eliminate the potential for adverse effects. The use of reversal agents can shorten recovery time and reduce the physiological impacts of anaesthesia but can also cause additional side effects. We, therefore, trialled the use of low-dose atipamezole (0.12 mg/kg) for the antagonism of xylazine in laboratory pigs anaesthetised using a combination of xylazine and zolazepam/tiletamine. We measured time to recovery, selected clinical variables, recovery characteristics, and behaviours to investigate if a low dose of antagonist decreased recovery time and reduced the physiological impacts of anaesthesia whilst avoiding adverse negative side effects. We categorised side effects and behaviours as having either a low or high negative welfare impact based on the potential risk of injury and whether behaviours were displayed before or after return to consciousness. Collectively, our results indicated that while the use of low-dose atipamezole decreased recovery time and improved thermoregulation in most pigs, it introduced and exacerbated adverse side effects and behaviours that can lead to poorer welfare outcomes for laboratory pigs. [ABSTRACT FROM AUTHOR]