July 16, 2017

Can Lameness Be Determined By a Horse's Facial Expression?

Early diagnosis of musculoskeletal pain in horses is key in preventing lameness and enabling optimal performance. How can a horse’s facial expressions help with early pain detection?
By Amy Bentz, VMD, DACVIM
Horses are used in a variety of disciplines, including competitive riding and racing, but there are times when they cannot be used for their intended purpose. This occurs, for example, when a horse has musculoskeletal pain, which can be difficult to detect until the horse shows significant lameness and poor performance. Nevertheless, early detection of musculoskeletal pain is paramount for horses’ welfare and successful treatment of their lesions, so they can achieve optimal performance.
 
Developing an Ethogram
Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, equine orthopedics specialist at the Royal College of Veterinary Surgeons, and colleagues developed an ethogram to describe facial expressions in horses being ridden; they described their study in November 2016 in the Journal of Veterinary Behavior. The researchers used previous publications and photographs of 150 lame and nonlame ridden horses to create a training manual for how to assess equine facial expressions.
 
In that study, 13 people from diverse backgrounds (including veterinarians, veterinary technicians, horse owners, equine studies graduates, and a British Horse Society instructor) were trained on how to assess facial expressions in horses. They then evaluated lateral photographs of 27 horses’ heads during training. The presence of horses’ features was graded, with possible answers being “yes,” “no,” or “cannot see” (if it was impossible to determine whether the feature was present), then the researchers adjusted the ethogram.
 
After additional training, the assessors blindly evaluated 30 heads of horses that were either lame or not lame. The mean interrater agreement was 87%. While the mean percentage of overall agreement for the assessors was 80%, there was a large standard deviation due to inconsistency in their assessment of the horses’ eyes and muzzle. The researchers concluded that the facial expression ethogram specific for ridden horses (FEReq) could be used by people with different backgrounds in the horse industry to describe horses’ facial expressions while being ridden.
 
Can Musculoskeletal Pain Be Diagnosed with the Ethogram?
Dr. Dyson and colleagues published a second study in the Journal of Veterinary Behavior in March 2017 to evaluate whether musculoskeletal pain could be determined from the facial expressions of ridden horses. Their aim was to determine whether the FEReq ethogram could be adapted to a pain scoring system for ridden horses. The study had 2 objectives:
  1. To assess differences in FEReq scores between still photographs of lame and sound (nonlame) horses’ heads while the horses were being ridden
  2. To use the observations to develop a pain score
 
A trained analyst, who was an equine veterinarian with additional training in equine behavior, used the FEReq and customized training manual to blindly evaluate 519 photographs taken while the horses were ridden at a trot and canter. The photographs showed each horse’s head and neck for 76 lame and 25 nonlame horses. The photographs included “before and after” images of 7 horses that were lame and then underwent diagnostic analgesia to eliminate the lameness.
 
A pain score was applied to each feature of the ethogram, and scores were higher in the lame group than the sound group. In addition, total pain score, head position score, and ear score were decreased in the lame horses after diagnostic analgesia. The best indicators of pain were twisting the head; ear position (both ears back, one ear forward and one backward, one ear to the side and one backward); open mouth with exposure of the teeth, severely above the bit; and eye features (eg, eyes partially or fully closed, tension caudal to the eye, intense stare). Sound horses were more likely to be on the bit with ears forward, eyes open, and lips slightly separated.
 
Based on the results of this study, a horse’s lameness status can be determined using the facial expression ethogram for horses being ridden (FEReq) and the pain score. The position of the horse’s eye, the facial expression, orbital tension in the muscles dorsal and caudal to the eye and whether the eyes were open or closed were significantly different in lame versus sound horses. However, the features of the ethogram should be considered in conjunction with the pain score, rather than just a single observation of one feature on the horse’s head while the horse is ridden.
 
In addition, the authors note that the “results apply to schooling-type work in the Olympic equestrian disciplines and are not necessarily transferable to other equestrian sports in which different head and neck positions are preferred. However, it seems unlikely that different head and neck positions should induce alterations in ear posture or the appearance of the eyes unless there was associated discomfort.”

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