Development and validation of a grimace scale for assessing pain in Angus beef calves

• Mostafa Farghal, Faculty of Veterinary Medicine, University of Calgary
• Ed Pajor, Faculty of Veterinary Medicine, University of Calgary
• Maria Camila Ceballos, Faculty of Veterinary Medicine, University of Calgary

Considering the lack of an appropriate on-farm pain assessment tool for beef calves, with this study we aim to develop and validate a grimace scale for assessing pain in Angus beef calves.

Sixty-nine Angus beef calves 6-10 weeks old were enrolled in this study: 34 surgically castrated and 35 subjected to sham castration. Videos of the face and behaviour were recorded for all calves at different periods: before, during and after castration and sham castration. Then, still images for the face (front and side views) were extracted and cropped. To identify different facial action units (FAU) related to pain, to compose the pain grimace scale, 240 images from all periods (from 10 sham and 10 castrated calves) were used.
Seven FAU were identified: backward ear, orbital tightening, tense stare, tension above the eye, dilated nostril, strained chewing muscle and open mouth. Convergent validation will be executed using whole-body behavioural videos before and after castration by applying UNESP-Botucatu unidimensional pain scale and evaluating the association between the two scales.

The inter and intra observer reliability will be evaluated as part of the validation process with 4 to 6 observers. Moreover, the internal consistency, accuracy, sensitivity, and specificity of the scale will be assessed. A practical, field-based tool for fast and accurate identification of pain in calves is important for veterinarian and practitioners’ pain mitigation decision. Therefore, a valid, feasible and reliable grimace scale would represent a good advance regarding pain assessment in beef calves.