That means a simple saliva test could denote horses whose bones aren’t coping well with training—and might risk breakdowns and catastrophic fractures—in addition to identifying training conditions, such as footing, that are harder on the bones, said Saritha Adepu, PhD, a researcher in the Department of Pathology at the Institute of Biomedical Sciences and Veterinary Public Health, part of the Swedish University of Agricultural Sciences in Uppsala.

“Our goal is to have a point-of-care biomarker that can aid horse owners and veterinarians to screen and monitor horses for the early signs of osteoarthritis,” she said.

Fragmented Bone Proteins: A New Biomarker for Bone Breakdown in Horses

Osteoarthritis is a leading cause of early retirement in athletic horses, Adepu said. Recognizing it in its earliest stages could lead to appropriate management that prevents career-ending injuries. Early osteoarthritis is usually silent, without apparent clinical signs, she said. The challenge is finding a way to detect osteoarthritis quickly and easily and, ideally, without costly, time-consuming, and sometimes invasive screening techniques such as imaging.

Looking for a solution, Adepu and her fellow researchers wondered if a protein called biglycan (BGN) might serve as a potential biomarker. BGN is a proteoglycan that’s expressed in both skeletal and non-skeletal tissues, but its most important role lies in bone structure, formation, and matrix mineralization, they said.

Because the neoepitope BGN²⁶² seems to result from microscopic bone breakdown, the researchers suspected it might also be associated with the early development of osteoarthritis. They thought it might reflect the quality of the footing horses were training on, as well.

It can be risky and invasive to extract biomarkers such as BGN²⁶² from synovial (joint) fluid, however, so the researchers wanted to determine if they could collect it from a less invasive source.

“BGN²⁶² is a small peptide that can diffuse easily into the body fluids,” Adepu said. “Therefore, we reasoned we would be able to detect it in saliva. And, if so, we wanted to see whether it reflected the synovial fluid levels. We further also aimed to have some sort of real-time measure for the impact of exercise/race training on the joints.”

Testing BGN²⁶² in Racehorses, Sport Horses, and Former Athletes With Osteoarthritis

To evaluate their theory, Adepu and her team members created a customized ELISA assay that detects and quantifies BGN²⁶² in saliva.

They then took saliva samples from nine former sport horses in Sweden with confirmed osteoarthritis as well as 19 healthy young Standardbred trotters without osteoarthritis that had started training one month prior.

Afterward, they took saliva samples from five privately owned sport horses in a Swedish stable at several time points before and after an intensive 20-minute workout plus warmup and cool-down time. Finally, they tested saliva from seven privately owned sport horses at a farm in Wellington, Florida, at several time points before and after exercising on two different footings, such as a sand-fiber arena and a sand arena.

To increase the sample size, the team also took saliva samples of 10 healthy research horses at their own institution at various time points during the day and night and especially before and after a meal to look for changes throughout the day or during feeding.

Osteoarthritis and Harder Ground Associated With Higher BGN262 Levels in Horses

The researchers found that BGN²⁶² levels were significantly higher in horses with osteoarthritis than those without, said Adepu.

In the exercise groups, BGN²⁶² began rising during warmup and peaked at the checkpoint after intense exercise. Levels started to lower during the cool-down period and returned to their pre-exercise rates within an hour after exercise.

When testing the healthy horses on different footing, they found that BGN²⁶² levels tended to be higher after the horses worked on the sand-fiber arenas. Mechanical testing showed the sand-fiber footing was harder and more compact, Adepu said. These findings line up with previous research showing the negative impact of harder surfaces on the musculoskeletal system, she added.

“The compactness and hardness of the ground surface can exert intense mechanical load on the joints, which on a long run can affect bone and cartilage tissue negatively, resulting in damage to the same,” Adepu told The Horse. “BGN²⁶² originating from the subchondral bone is extremely sensitive to the mechanical load experienced by the joints, the levels of which proportionally increase in the saliva of the horse during the intense exercise.”

In both tests with the privately owned sport horses, BGN²⁶² levels were higher in those with previous diagnoses of osteoarthritis, she said. “BGN²⁶² levels go up not only in the osteoarthritis group but also in healthy horses—but there are higher levels in osteoarthritic horses,” Adepu explained.

The researchers determined the BGN²⁶² levels in saliva reflect the concentrations of already-existing levels of the biomarker in synovial fluid, she explained. “During exercise, the soluble BGN²⁶² in synovial fluid mobilizes and diffuses quickly in the serum and saliva,” Adepu said.

Take-Home Message

While more research is necessary before making concrete recommendations about training regimens or footing, Adepu said she encourages owners to have their horses’ BGN²⁶² concentrations monitored.

The team’s next goals are to test surfaces with a larger number of horses and to create a point-of-care saliva test that can give instantaneous results in the field, said Adepu.

“The point-of-care could be of immense aid in diagnosing or screening a horse for early signs of osteoarthritis and can help in preventing catastrophic chip fractures that are detrimental to the horse,” she said.

“Measuring the levels longitudinally can help horse owners and their veterinarians assess the joint health status of horses from a very young age. This information can be useful in tailoring the race-training regime, as well as rehabilitation periods, for the horse.”