You have likely heard of the horse pain ethogram, which is a predictor of a horse’s discomfort based on a variety of facial and postural signs. Taking that a step further, researchers have established a relationship between the ridden horse pain ethogram and performance, even in the absence of overt lameness. At the 2022 American Association of Equine Practitioners Convention held Nov. 18-22 in San Antonio, Texas, Sue Dyson, MA, Vet MB, PhD, DEO, Dipl. ECVSNR, FRCVS, presented a variety of studies demonstrating this connection.
The ridden horse pain ethogram (RHpE) describes 24 behaviors. Most are 10 times more likely to be identified in a lame horse than a sound one, said Dyson. Common behaviors include:
- Ears pinned back for at least (≥) five seconds.
- Glazed stare or expression for at least five seconds.
- The front of the head at least 10 degrees behind the vertical position for at least 10 seconds.
Dyson explained that a horse demonstrating 8 of 24 ethogram behaviors is likely experiencing musculoskeletal pain. A relationship between pain and behavior is corroborated when RHpE behaviors diminish after diagnostic nerve or joint blocks relieve lameness.
Based on examining highly-trained horses at five-star events, Dyson recommended using a slightly lower total RHpE score of 7 as an indicator of influence on performance. In one study conducted at the 2018 Burghley Horse Trials, researchers assessed 35 horses for 10 minutes in a dressage warm-up. Horses were classified as non-lame, lame, or having a stiff, stilted gait at trot or canter. Elimination at cross-country occurred in 67% of horses with RHpE scores > 7 compared to 29% of horses with RHpE scores of < 7.
At World Cup Grand Prix dressage competitions, the median RHpE score of 147 horses evaluated was 3/24 (range of 0-7). Researchers noted a high frequency and duration of mouth opening with teeth separation in 68% of horses, head behind the vertical in 56%, an intense stare in 30%, and repeated tail swishing in 29%. Tail swishing also occurred in synchrony with the rider’s spur taps in 36%.
Dyson described non-lame horses at three other eventing venues as having a median RHpE score of 3, while those with gait abnormalities had median scores of 5 at trot or canter. The most common findings (lasting ≥ 5 or 10 seconds) were the head behind the vertical in 64%; repeated head tilt in 56%; mouth open with teeth separated in 44%; intense stare for in 38%; and tail swishing in 38%. Horses with RHpE > 7 were assigned more dressage penalties and more likely to be eliminated or retired on the cross-country phase or finish in lower places. Of 172 starters, 63% with RHpE > 7 failed to complete the cross-country phase compared to 31% with scores < 7. Horses that start out compromised on the cross-country course require more effort to clear fences and are less able to adjust for problems, she said.
Even lower-level competitions reveal a relationship between RHpE and performance, said Dyson. At a one-day eventing venue, 1,010 horses were assessed during a five-minute dressage test, then jumped fences of 3, 3.3, or 3.6 feet. Dressage penalty scores correlated to RHpE scores at all levels. Horses placing in the top three spots had lower RHpE scores (median 2/24) than other finishers (4/24). Notably, lower-level horses had a higher frequency of overt lameness or gait abnormalities at canter compared to five-star competitors.
Riding with a horse’s head behind the vertical (one of the RHpE behaviors) reflects not only incorrect training methods but also musculoskeletal pain, said Dyson. Consequences of this behavior include:
- Decreased muscle engagement.
- Decreased range of motion of the thoraco-lumbar-sacral region.
- Decreased development of epaxial muscles along the spine.
- Decreased hind-limb engagement and impulsion.
- Increased risk of injury.
Dyson noted that judges seem to reward horses with higher RHpE scores, citing a horse with an RHpE of 5 that scored 82%. With this in mind, she recommended judges be more honest in their assessments and penalize incorrect performances, while riders and trainers should recognize what normal and correct movements look like. A horse tends to stiffen its back more when ridden from hand to leg rather than the correct method of leg to hand. Dyson emphasized that rider skill can influence a horse’s gait quality and performance but cannot reduce the number of behaviors exhibited by a horse experiencing discomfort.
Veterinary involvement can help improve horse welfare and safety through performance health checks that include ridden exercise and RHpE scores. Dyson stressed that riders should use warm-up periods for warm-up, not training, and should avoid asking for movements their horses find difficult, such as flying changes. She further pointed out that pain-free horses are more trainable, as well as safer.
