The development of a facial expression scale using footrot and mastitis as models of pain in sheep

Abstract

Management of pain in sheep is limited by the challenges of recognising and accurately quantifying 35 pain in this species. The use of facial expression scoring to assess pain is a well-utilised, practical tool 36 in both humans and non-human animals. The objective of this study was to develop a standardised 37 facial expression pain scale for adult sheep, that could be used reliably and accurately to detect pain 38 associated with naturally occurring painful diseases, such as footrot and mastitis. We also investigated 39 whether the scale could be reliably and accurately utilised by observers after training, enabling the 40 development of an on-farm pain assessment tool. The Sheep Pain Facial Expression Scale (SPFES) 41 was able to correctly identify sheep suffering from disease with a high degree of accuracy (AUC; 42 Footrot: 0.81, Mastitis: 0.80). Diseased sheep scored higher on the scale than controls on the day of 43 disease identification (P<0.05) and diseased sheep showed changes in their facial expression after 44 treatment (P<0.001). The abnormal facial expressions of diseased sheep reduced over time, and at 45 recovery were in line with control sheep. Control sheep did not change their facial expression over 46 time. Five scorers who were trained to use the developed scale also assessed the facial expressions of 47 sheep. The scorers were blind to treatment and session. Scorers reliably (ICC: 0.86) and accurately (α 48 = 0.86) identified changes in the facial expression of sheep with footrot over time (P<0.05), and 49 scored control sheep consistently low over time. The SPFES offers a reliable and effective method of 50 assessing pain in sheep after minimal training.