Do horses referred for mild lameness show any facial expressions of pain and behavioural issues at rest?

In horses, timing of diagnosis and treatment of orthopaedic disorders importantly affect their prognosis. Behavioural modifications are initial signs of a painful condition and can possibly help the veterinarian in making an early diagnosis and address the clinical suspect. This study aimed to investigate whether horses referred for mild lameness showed, at rest, any modifications in behaviour or facial expression that can help recognising a painful condition. Two groups of sport horses balanced for age, sex and training activity were included in a case-control study: mild lameness group (N=10) horses referred for lameness considered as “mild” because not seen in every stride (AAEP lameness scale: score 1 or 2), and control group (N=15) clinically sound horses. Owners were asked to fill out a questionnaire about behaviour shown by horses during exercise and daily management. Specifically, they were asked on a 4-point scale to report the frequency (from never to always) their horse was reluctant to move or showed signs of discomfort on specific type of soil or gait, signs of aggression or fear when groomed or saddled. For each horse, 1 min video was recorded when the animal was at rest in their box and later assessed by a group-blind observer using the Horse Grimace Scale (HGS), a facial-expression–based pain coding system including six Facial Action Units (scored from 0 to 2) [1]. The observers attended a specific training period until they reached an excellent level of inter-observer agreement. Mann-Whitney test was used to assess differences between groups. 50% of mildly lame horses were reported to be “sometimes” fearful (e.g., avoid) and aggressive (e.g., bite or kick) towards people, significantly more compared to the control group (CI 0.03-0.35; P=0.036); they were also reluctant to be saddled, avoiding or reacting in an aggressive way (always=10%; often=10%; sometimes=50%) (CI 0.12-0.73; P=0.005). The HGS score was significantly higher for mild lame horses (3.1+/-1.8) compared to control ones (1.2+/-1.2) (CI 1.18-2.65; P=0.015). These results suggest that systematically assess changes in behaviour and facial expressions can be helpful to get an early warning of mild orthopaedic disorders. Including a HGS assessment after diagnostic block is suggested for further validation of the results. References: 1. Dalla Costa et al.,(2016) Using the Horse Grimace Scale (HGS) to Assess Pain Associated with Acute Laminitis in Horses (Equus caballus). Animals, 6 (8), 47.