Equine lameness can be difficult to detect, but a study from England confirms the reliability of a relatively new tool for identifying subtle signs of musculoskeletal pain in horses.
Developed at the Animal Health Trust in Newmarket in 2018, the Ridden Horse Pain Ethogram (RHpE) is a compilation of 24 behaviors, such as “head tilting,” “tail swishing” and “spontaneous changes of gait,” that have been proven to correlate with musculoskeletal pain (see “A System for Identifying Lameness,” below). If a horse exhibits eight or more of the behaviors, chances are good he is lame.
Undiagnosed lameness has a far-reaching impact on the lives of horses and their riders, says Sue Dyson, VetMB, PhD. “One of the reasons I was incentivized to develop a RHpE was I had become so dispirited by seeing so many horses who clearly had pain-related problems that had been ignored for far too long,” she explains. “The horse, the rider, the training technique were being blamed over and over again. Coercive training techniques were being used. Longer whips, spurs, tighter nosebands, ‘stronger’ bits were being employed. Moreover, veterinarians did not understand what they were looking at either---if an enlightened owner sought advice, and there was no obvious lameness seen in hand, they were told that the horse had behavioral problems.”
In early research, most of the behaviors on the RHpE were found to be 10 times more likely to be seen in lame horses, and they were eliminated by measures that relieved pain---such as nerve blocks---which verified their association with discomfort.
For the most recent study, researchers selected 60 horses considered sound by their owners. The average age of the horses was 11 and they were used in a variety of English disciplines. Eleven were lesson horses at a riding school.
At the beginning of the study period, the horses were examined by a physiotherapist for signs of back pain. A master saddle fitter then checked the fit of each horse’s tack to determine if it could be a source of pain. Each horse was then ridden by his usual rider through a dressage-type test that included walking, trotting, cantering and circling in both directions. An experienced veterinarian observed each ridden test and evaluated the horse for lameness, assigning a score on a 0-to-8 scale. The tests were also videotaped from two angles.
Next, a second researcher, unfamiliar with each horse’s lameness score, analyzed the videotapes, documenting any instances of the behaviors listed in the RHpE. Finally, a third researcher watched the videotapes and scored each rider’s skill on a scale of 1 to 10.
The combined data showed that the presence of eight or more behaviors listed on the RHpE correlated with a lameness diagnosis by the veterinarian who observed the ridden test—confirming the findings of the earlier research. The behaviors that had the strongest statistical correlation with lameness were ears being pinned back for five seconds or more, an intense stare for five seconds or more and repeated stumbling or dragging of both hind toes.
The researchers also found that almost three-quarters of the horses (73 percent) that were assumed to be sound by their owners actually had some degree of lameness. Dyson says this result isn’t particularly surprising, given that many of the behaviors on the RHpE are often dismissed as “normal” by riders. “I’ve lost count of the times that clients have said to me, ‘He’s always found it difficult to canter—that’s normal for him’,” says Dyson. “Or, ‘He’s never been a very willing horse ever since I bought him,’ or ‘he always comes out a bit stiff.’”
An even higher pro-portion (82 percent) of the study’s lesson horses were found to be lame by the researchers, who noted that this group also had the highest median RHpE scores.
“When I think back to my childhood and think of all the horses at my local riding school, where I spent all my spare hours, and how these horses behaved, I don’t think this is a new phenomenon,” says Dyson. “One of the reasons that some of these horses are so safe for beginners is that they don’t want to go quickly; they hold their backs stiffly to compensate for lameness and minimize their discomfort, making them easier to ride. With a bigger range of motion they would be more difficult to ride.”
She adds that a few simple management changes could help keep lesson horses more comfortable: “I’d like see better use of pain-relieving medications such as phenylbutazone, and more lessons on a mechanical horse to establish basic position and balance, so that beginner riders are better able to ride bigger-moving, less lame horses,” Dyson says. “And more attention paid to better-fitting saddles for horses and riders. Although not significant in this study, we have done another study ready for publication in which we found that tight tree points can affect the RHpE, as does the rider sitting on the back of the saddle versus the middle of the saddle.”
Overall, any horse who displays eight or more RHpE behaviors needs a full lameness workup, says Dyson, “although, sadly, non-specialist veterinarians may currently not have the skills to investigate properly.”
Reference: “Application of a Ridden Horse Pain Ethogram and its relationship with gait in a convenience sample of 60 riding horses,” Animals, June 2020
A system for identifying lameness
The Ridden Horse Pain Ethogram (RHpE) was developed by Sue Dyson, VetMB, PhD, in 2018 to help detect lameness.
If a horse exhibits eight or more of the following 24 behaviors, it is likely that he is experiencing musculoskeletal pain.
1. Repeated changes of head position (up/down), not in rhythm with the trot
2. Head tilted or tilting repeatedly
3. Head “in front of vertical” (more than 30 degrees) for 10 seconds or more
4. Head “behind vertical” (more than 10 degrees) for 10 seconds or more
5. Head position changes regularly, tossed or twisted from side to side, corrected constantly
6. Ears rotated back behind vertical or flat (both or one only) five seconds or more; repeatedly lay flat
7. Eyelids closed or half-closed for two to five seconds; frequent blinking
8. Sclera (white of the eye) exposed repeatedly
9. Intense stare (glazed expression, “zoned out”) for five seconds or more
10. Mouth opening and/or shutting repeatedly with separation of teeth, for 10 seconds or more
11. Tongue exposed, protruding or hanging out, and/or moving in and out repeatedly
12. Bit pulled through the mouth on one side (left or right) repeatedly
13. Tail clamped tightly to middle or held to one side
14. Tail swishing in large movements: repeatedly up and down/side to side/circular; repeatedly during transitions
15. A rushed gait (frequency of trot steps great than 40 per 15 seconds); irregular rhythm in trot or canter; repeated changes of speed in trot or canter
16. Gait too slow (frequency of trot steps less than 35 per 15 seconds); passage‐like trot
17. Hind limbs do not follow tracks of forelimbs but repeatedly deviate to left or right; on three tracks in trot or canter
18. Repeated lead changes at the canter in front and/or behind; repeated strike off on wrong lead; disunited
19. Spontaneous changes of gait (e.g., breaks from canter to trot, or trot to canter)
20. Stumbles or trips more than once; repeated bilateral hind-limb toe drag
21. Sudden change of direction, against rider’s direction; spooking
22. Reluctance to move forward (has to be kicked and/or given verbal encouragement); stops spontaneously
23. Rearing (both forelimbs off the ground)
24. Bucking or kicking backwards (one or both hind limbs