Müller, B. R., Souza Soriano, V., Biscarra Bellio, J. C. et al. 2019. Facial expression of pain in Nellore and crossbred beef cattle. Journal of Veterinary Behavior 34, 60-65.

Although the science of facial expression of pain in humans is advanced, it has not been extensively explored in nonhuman animals. The study of facial expression as an indicator of pain might represent a substantial advance in pain recognition and management in other species, not yet studied. The main objective of this work was to investigate whether specific facial action units (AUs), previously related to painful facial expressions in human and some nonhuman animals, are also activated in beef cattle during acute painful stimulation. The study also investigated whether specific facial AUs of beef cattle in acute pain differed by sex and two genotypes. The activation of AUs was examined through pictures of a total of 35 beef cattle before and during branding with a hot iron, characterizing moments of no-pain (N) and pain (P). There were 17 female and 18 male beef cattle of two different genotypes: Nellore and crossbred (1/2 Nellore, 1/4 Bonsmara, 1/8 Red Angus, and 1/8 Aberdeen Angus). Results showed no differences in activation of AUs between males and females, and a higher frequency of mouth opening in the crossbred animals. The activation of the AUs backward ears, dilated nostril, open mouth, raised inner brow, and raised outer brow were significantly associated with the presence of the painful stimulus and should be considered for the development of further pain assessment methods using facial expressions for this species. The higher proportion of open mouth reactions in crossbred compared with Nellore cattle in response to an acutely painful stimulus indicates the importance of considering genotype when assessing pain by facial expression in cattle. As more detailed information becomes available, the on-farm use of facial expression to recognize pain in cattle may override some of the difficulties in animal pain diagnosis and, consequently, allow for rapid and consistent intervention to ameliorate suffering.