For years now, researchers have been searching for some kind of agent detectable in horses' blood to warn them of an impending injury. Research presented by Dr. David Horohov of the Gluck Equine Research Center at the University of Kentucky at a recent Kentucky Equine Drug Research Council meeting shows the quest has continued to be a challenging one.
“The theory has been advanced that in fact, visible injury is a result of chronic accumulation of damage that exceeds the healing capacity of the tissue. And indeed, the whole process of conditioning an animal is actually one of breaking down and rebuilding tissue so that it's stronger,” said Horohov. “If we could identify techniques to tell when that process has become imbalanced, where there is weakness rather than strength, we could begin identifying horses in advance.”
Initially, Horohov said scientists wanted to look for cytokines – biological message-carriers – associated with damage to bone and cartilage. This proved challenging because bones are constantly in a cycle of breaking down and building up in response to exercise. It is the remodeling process that prepares an equine (or human) skeleton to hold up to future impacts, based on past experience. This approach also did not seem sensitive enough and might miss other types of stress in the body, so Horohov set out to study the behavior of cytokines related to inflammation.
These messengers would be aware the body was recruiting inflammatory cells to deal with an injury but would not be involved in the inflammatory process themselves. Theoretically, he thought, low levels of inflammatory cytokines should indicate some degree of normal response to training, while high amounts might be a sign the body was not adjusting to the stress of training, increasing the likelihood of an accident.
Between 2015 and 2016, Horohov and his team studied two groups with a total of 130 horses over two years: one group, scattered across different trainers, at Keeneland's synthetic training track, and another group on a lighter workout program (working on turf once per week) on a nearby farm. The results were somewhat surprising.
Immediately after exercise, horses typically have an increase in inflammatory biomarkers, which come back down over time and usually go below their original level – thought to be a sign the horses' tissues were adjusting to exercise. Horohov's group did find a difference between the horses at the track and those trained on the farm – over time, horses training on the track saw their base level inflammatory index increase, rather than decrease.
“To us, this raises more questions than it answers,” he said.
Horohov said it was impossible to tell whether the increase in inflammatory index was a sign of an increased risk for injury, or if it was simply a normal response to training. Both groups of horses had just begun the process of breezing.
Horohov also hopes in the future, the study of inflammatory cytokines could be finessed to predict specific types of injuries.
Besides the somewhat puzzling results, studies like this one are challenging because in order to get a group of horses in a true racetrack setting, scientists must give up control of the horses' environments. Across the group of 130 horses studied, many were with different trainers and different feeding programs (including different supplements); those on the farm were getting turnout, while those at the track were not. It's difficult to draw broad conclusions when variables like these place horses in mini sub-groups.
“One of the problems, too, about sampling horses is they leave,” said Horohov. “You get something you're really interested in, you go back and they're not there anymore.”
Horohov estimated about 25 percent of horses came up with some kind of lameness during the study period, but they were split between so many different trainers and programs it was impossible to say with certainty whether their cytokine levels rose before their lamenesses, or when.
From here, Horohov's team hopes to expand the study to try to minimize some of these variables and to see whether an exaggerated inflammatory response does, indeed, preempt injuries.
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