veterinarian watching horse jog

If you’re checking for lameness, it’s critical to keep the slope of the ground in mind.

Even a very slight slope can affect the way horses move and how lame they appear—especially in cases of hind-limb lameness. That doesn’t mean lameness exams always have to occur on flat ground, however. On the contrary, a minor slope can help expose lameness—provided the practitioner is aware of its effects, said James Bailey, BVetMed, FHEA, MRCVS, clinical assistant professor in veterinary sports medicine at the University of Nottingham’s School of Veterinary Medicine and Science, in the U.K.

“We’re talking about really not a huge slope at all—and in our study it wasn’t particularly steep—but it still managed to make some pretty big differences going uphill versus down versus the flat,” Bailey said. “You can’t just assume that from your one end of the trot-up, you’re doing a good enough job.”

Bailey became curious about the effects of slight slopes when working with a particular case of hind-limb lameness in which the horse had significant muscle wastage on one side. As is often the case with real-life veterinary exams, the only trot-up area involved a slope—albeit relatively minor.

“I realized the horse was lame on the left hind going away from me, and he was lame on the right hind coming back toward me,” Bailey said, adding that he was only watching from one end of the trot-up.

“This case triggered me to think, ‘Well hang on, how many more lameness cases are we missing here due to the trot-up conditions in the field?” he told The Horse.      

Trotting 17 Lame Study Horses on a 2.4% Slope

Inspired by that experience, Bailey and his fellow researchers used inertial movement sensors (IMUs) to assess 10 horses diagnosed with forelimb lameness and seven horses with hind-limb lameness. They placed the IMUs in five places: the withers, poll, sacrum, and both hip points. All horses were Irish sport horses older than 7 years with mild (Grade 1 or 2 out of 5), naturally occurring lameness; they had been admitted to an equine referral hospital for investigation.

The researchers trotted the horses in two directions on a relatively flat asphalt surface (with a 0.7% slope maximum) and on a slightly sloped (2.4%) asphalt surface. The percentage represents the difference of the ground relative to the true horizontal.

Based on 25 strides of data in each direction, the researchers determined that horses with hind-limb lameness showed about 50% more asymmetry when going up the slight incline than when on a flat surface, he said. Going downhill, though, the horses showed only a quarter of the asymmetry they displayed on the flat surface.

As for the 10 horses with forelimb lameness, the scientists found no particular trends in the group, Bailey said. Even so, individual horses varied significantly in their reaction to the upward and downward slopes.

The reason might be the type of lesion causing the lameness in these horses, he said. The researchers’ small sample size and the human coronavirus pandemic at the time of the study—which prevented more in-depth studies—did not allow them to make reliable scientific conclusions about the effects of specific lameness causes on asymmetry seen on slopes. In the future, Bailey said he’d like to describe uphill versus downhill reactions in cases of different types of tendon or foot diseases.

Slopes Can Hinder and Help Lameness Evaluations

The findings suggest having a flat surface might provide a useful standard for lameness evaluations, but an incline could add feedback useful for understanding lameness, said Bailey.

“In the ideal world you’d have everything, wouldn’t you?” he said. “You’d have a flat surface, a sloped surface, an incline this way, an incline that way. But nobody’s going to have all of those things. So understanding the limitations and the benefits of imperfect surfaces is really important.”

Another critical take-home message of his study, he added, is lameness exams on even slight slopes must be carried out from both directions.

“Even if you think the slope is not too severe, you need to be strict with yourself in saying actually, ‘No, I need to watch this from both ends,’” he said. This includes prepurchase exams in field conditions, he added.

That Not-Right Feeling Owners Get on Slopes: ‘Could Be Lameness’

On a grassroots level, the findings also suggest that even owners might pick up on lameness issues—especially hind-limb lameness—based on their horses’ behavior on different slopes, said Bailey.

“If you’re out riding, for instance, on a hack, and you come down a slope at a trot and you think, ‘Oh wow, that felt peculiar,’ and then you go home and get a friend to trot your horse up and down a straight flat line and think he’s fine, the truth is he might not be,” Bailey said.

Riders could even suggest to their veterinarians that they return to the same slope to see what was happening there, he added. “Show what feels strange to you, because I think mostly likely based on this, it could be a sign of lameness,” he said.

The article, An objective study into the effects of an incline on naturally occurring lameness in horses appeared in the Veterinary Medicine and Science in August.