With the increase in attention to animal welfare, researchers have focused their interest on the assessment of pain in farm animals. In humans who cannot self-report, such as infants and unconscious patients, the observation of facial expression is frequently used for pain assessment (Prkachin, 2009). The possibility to assess pain through changes of facial expression has also been studied in animals, and pain scales developed which include the ‘Mouse Grimace Scale’ (Langford et al., 2010), the ‘Rat Grimace Scale’ (Sotocinal et al., 2011) and the ‘Rabbit Grimace Scale’ (Keating et al., 2012). Although with some species differences, the three scales focus on the eyes, nose, cheeks, ears and whiskers of an animal.
Although pigs have fewer muscles for facial expression, there are subtle changes in appearance (Flecknell & Watermann-Pearson 2000), but there are currently no published pain scales based on facial expression in pigs. The aim of this research was to investigate if it is possible to observe changes in piglets’ facial expressions immediately after painful procedures. Thirty-one piglets were subjected to tail docking by cautery, while held by the farmer. Images of faces were taken immediately before and after this procedure. These images were sorted and those in which piglets had closed eyes were excluded.
Images were evaluated by two treatment-blind observers, scoring from 0 to 2 (0 was no evident tension and 2 very evident tension).
Because of the non normal distribution, data were analysed with the non-parametric Wilcoxon Signed Rank Test, which showed that the cheek tension score significantly increased from before to after the procedure (P<0.042). This result shows promise for the adoption facial expression as a tool for acute pain assessment in pigs.
In piglets subjected to tail docking cheek tension score significantly increased from before to after the procedure (P<0.05)
Reference: Lonardi, C., Leach, M., Gottardo, F., Edwards, S. 2013. The ‘Grimace Scale’: do piglets in pain change their facial expression? Proceedings of the Joint Meeting of the 5th European Symposium of Porcine Health Management and the 50th Anniversary Meeting of the Pig Veterinary Society of Great Britain, Edinburgh, UK, 22nd – 24th May 2013.