Is the Piglet Grimace Scale (PGS) a Useful Welfare Indicator to Assess Pain after Cryptorchidectomy in Growing Pigs?

SIMPLE SUMMARY: On farms, pigs undergo husbandry procedures that can be painful. However, pain assessment in pig farming faces practical limitations, pertaining to the lack of reliable and feasible tools. This work aimed to investigate whether the Piglet Grimace Scale (PGS), a facial-expression-based pain coding system, could be usefully applied to assess pain associated with on-farm surgery in growing pigs. Ten pigs affected by cryptorchidism (a congenital anomaly which requires surgical intervention) were assessed before and 6 h after surgery. The authors found that the PGS score increased after surgery, and therefore, that the PGS is a potentially effective method to assess pain associated with surgery in growing pigs. ABSTRACT: Pig cryptorchidism is a congenital anomaly, which requires surgical intervention. Pain assessment in pig farming has some limitations and consumers are increasingly concerned about suffering linked to on-farm procedures. The PGS seems to be a promising tool for pain assessment in piglets, although it has not been investigated whether this tool is applicable to growing pigs. This study was designed to determine whether the PGS could be useful to assess pain in growing pigs undergoing on-farm cryptorchidectomy. Ten mixed-breed cryptorchid pigs were pre-medicated with azaperone and ketamine. Anesthesia was induced and maintained using IV sodium based. Pigs were filmed pre- and 6 h post-surgery to evaluate their behavior (scan sampling every minute). Besides, 36 pictures of the face expressions (18 pre- and 18 6 h post-surgery) were scored with the PGS by three treatment-blind observers. The pre-surgery pig’s activity ratio was 59%, while it was 2% 6 h post-surgery. While the PGS inter-observer reliability was excellent (Interclass Correlation Coefficient value of 0.87), the PGS score increased significantly in pigs 6 h post-surgery (Paired sample t-test, p = 0.02). The PGS proved to be a potentially effective method to assess pain associated with cryptorchidectomy. However, further validation studies are required to validate this tool for other potentially painful procedures.