New way to assess pain

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A new method of assessing pain in horses offers an easier, safer and more humane way of evaluating cases of acute laminitis.

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Caused by physical or physiologic injury, laminitis is an excruciating inflammation of the soft issue within the hoof. Walking or jogging a horse with acute laminitis to gauge lameness or soreness can be difficult and may exacerbate damage to internal structures of the feet. Now, however, a group of collaborating researchers at Havelland Equine Clinic in Germany, University of Milan in Italy and Newcastle University in United Kingdom have developed a so-called “grimace scale,” which uses the intensity of specific facial characteristics to estimate a horse’s level of pain.

The technique, which originated in human medicine, has previously been adapted to evaluate pain in mice, rats, rabbits, cats, sheep and other animals, says Emanuela Dalla Costa, DVM, PhD. “Facial expressions are commonly used to assess pain and other emotional states in humans who are unable to communicate coherently with their clinicians, such as babies,” she says, adding, “In particular, facial expressions seem to be useful in animals that tend to hide signs of pain in the presence of predators.”

To determine the efficacy of the Horse Grimace Scale (HGS), researchers videotaped 10 horses admitted to the Havelland clinic between 2012 and 2014 for acute laminitis. The horses were recorded for 20 minutes on the day they were admitted and again seven days into their treatment, which consisted of anti-inflammatory medications, submersion in ice water, padded hoof bandages with frog support and restricted movement in a stall with deep bedding. 

Next, the researchers randomly selected two still frames of each horse from both filming sessions and asked four unaffiliated veterinarians to score them according to the HGS. The still images clearly showed the horse’s faces and the veterinarians were instructed to assess six different facial actions associated with pain, including pinned ears, tension around the eye area, and strained chewing muscles, nostrils and mouth. Each action was scored on a two-point scale, 0 for “not present,” 1 for “moderately present,” and 2 “obviously present.” They also gave a final score for overall inten-sity of pain, from 0 for no pain to 3 for severe. 

For comparison, each horse was also given an Obel score on the first and seventh day of treatment. The Obel grading system assigns a number based on the amount of lameness a horse shows as he is being walked or jogged, from 0 to indicate no gait abnormalities to 4, indicating non-weight bearing or significant reluctance to move.

When researchers compared the two sets of scores, they found that the HGS was very reliable in identifying horses with high Obel scores, which veterinarians classified as being in more severe pain. The researchers note that using HGS to evaluate pain could improve the welfare of horses with acute laminitis by eliminating movement necessary for other assessments. 

Dalla Costa emphasizes that HGS is simple enough for horse owners to use and an instructional application for Android devices can help guide them.

Reference: “Using the Horse Grimace Scale (HGS) to assess pain associated with acute laminitis in horses (Equus caballus),Animals, August 2016 

This article was originally published the February 2016 issue, Volume #473 of EQUUS magazine

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