Gauging Pain in a Lame Horse at Rest

Asymmetry of movement remains a telltale sign of lameness, likely due to discomfort or pain. Have you ever stopped to wonder how much pain a lame horse experiences while standing casually in its stall or paddock?

A Swedish research team recently asked this question. The team compared four different pain scales using eight healthy horses with experimentally induced, temporary orthopedic pain.^*

Lameness examinations and pain assessments were performed prior to the joint injection, during the short-term inflammatory period, and several times during and after resolution of joint inflammation.

Four different pain scales were used in this study: Horse Grimace Scale, Equine Utrecht University Scale of Facial Assessment of Pain, Equine Pain Scale, and Composite Orthopedic Pain Scale (COPS).

“These scales use various assessments of facial expressions, behaviors, and physiology variables to create a ‘pain score’ for the horse,” explained Kathleen Crandell, Ph.D., a Kentucky Equine Research nutritionist.

Lameness was assessed objectively by placing spherical markers on the horse and infrared motion capture cameras. Experienced equine practitioners also subjectively evaluated each horse.

“The study showed that COPS was the most reliable scale, indicating significant associations between total pain score and total movement asymmetry score. This scale used more than just facial expressions to assess pain, as facial expressions may be more challenging to interpret for some observers than body postures or behaviors,” Crandell said.

Researchers found some pain scores to be 0 after induction of joint inflammation. “The researchers suggested that these horses may not have continuously experienced pain at rest or they were able to adjust their weight, limiting the load on the painful limb. As a result, their pain score decreased. The researchers also cited a study in which horses hid their discomfort when evaluators were present,” Crandell explained.

The researchers also noted that these scales may not be valid for different types of pain or even different types of orthopedic pain. In other words, the amount of pain a horse experiences at rest after surgery may not be the same as what a laminitic pony experiences.

“The study results suggest that a pain assessment tool applied in resting horses used in conjunction with lameness examination grading may help decide the pain level of orthopedic patients. Having this information ensures horses receive appropriate pain control,” said Crandell.

In addition to anti-inflammatory medications, a staple in managing orthopedic patients, experts recommend adding oral joint health supplements to help support joint health for those horses.

“For joint comfort, supplementing with hyaluronic acid (HA) may help lubricate joints. Synovate HA helps maintain cartilage health and elasticity, joint fluid viscoelasticity, and lubrication of the entire joint mechanism. Further, HA has anti-inflammatory properties, which are useful for high-motion joints,” summarized Crandell.

Additional information regarding the COPS scales is available in the following study: Bussières, G., C. Jacques, O. Lainay, G. Beauchamp, A. Leblond, J.-L. Cadore, L.-M. Desmaizieres, S.G. Cuvelliez, and E. Troncy. 2008. Development of a composite orthopaedic pain scale in horses. Research in Veterinary Science 85:294-306.

 ^*Ask, K., P. Haubro Andersen, L.-M. Tamminen, M. Rhoden, and E. Hernlund. 2022. Performance of four equine pain scales and their association to movement asymmetry in horses with induced orthopedic pain. Frontiers in Veterinary Science 9:938022.