Two restraining devices in connection to surgical castration with or without local anesthesia: effects on piglet stress.

backgroundSurgical castration causes severe pain to young piglets. In addition, piglets experience intense stress from handling and restraining during the procedure. Furthermore, piglets must be restrained twice when receiving local anesthesia before castration, and the injections are painful. Unfortunately, strategies to reduce piglets' stress during handling, local anesthetic injections, and painful procedures are limited and poorly understood. Thus, we randomized 179 male piglets aged 3 to 4 days to be restrained with either a commonly used commercial tubular bench with a dorsal restraining posture or a custom-made castration rack with a vertical restraining posture. Piglets received local anesthetic or sham injections (mimicking local anesthesia but without skin penetration) 10 min before castration. We then compared the effect of these devices on the piglets' behavioral reactions, vocalizations, and body temperatures at the following four times: when restrained for the first time, when given local anesthetic injections or receiving sham injections, during the second time restrained, and during castration.

resultsPiglets were given higher mean reaction scores when restrained in the tubular bench than the castration rack. Piglets showed differing vocalization patterns in the two devices, with more grunts and screams in the castration rack and more squeals in the tubular bench. Moreover, local anesthetic injections resulted in higher mean reaction scores and longer vocalizations than sham injections during the injections/sham injections but reduced these measures during castration. After castration, the skin temperature was higher in sham-injected piglets than in piglets castrated with local anesthesia, irrespective of the restraining device used.

conclusionsLocal anesthesia reduced piglets' reaction scores and vocalizations during castration. However, receiving local anesthesia was painful. Based on piglet behavior, restraining in a tubular bench was more aversive than in the castration rack. However, the devices affected the proportions of the different vocalization types during local anesthetic injections and castration in a manner we cannot fully explain. As the restraining method affects piglets' behavior, it may influence pain assessment during local anesthetic injections and evaluation of local anesthesia efficacy during castration. Thus, less stressful methods to handle piglets are needed.