fatal injuries in racehorses | Horse Racing Free Tips

As the quest continues for a better way to identify racehorses at risk for fatal injury, a study from the University of Kentucky's Gluck Equine Research Center may provide scientists and veterinarians a roadmap of where to look. At a regularly scheduled meeting Oct. 22, the Kentucky Horse Racing Commission received initial results from a study by Gluck researchers Dr. Allen Page and David Horohov looking at inflammatory biomarkers. Biomarkers are proteins, which can be produced at different levels in the body depending on changes and normal processes like inflammation.

Researchers have looked at biomarkers before to try finding some that would signal inflammation that may still be subclinical, or not producing recognizable symptoms yet in the horse. Previous efforts have yielded mixed results, in part because the body undergoes some amount of normal inflammation in response to exercise even when the horse isn't battling an underlying injury. Other biomarkers don't show up until the injury occurs, which makes them useless from a predictive standpoint.

Thanks to funding provided by the Kentucky Equine Drug Research Council (KEDRC), Page and Horohov are in the midst of a two-phase research project — the first looking at a new set of biomarkers and the second looking at messenger RNA, which signals the production of proteins like biomarkers. The second phase is still in progress, and Tuesday's meeting focused on the results from the first phase.

Page and Horohov gathered data from racetracks in four racing jurisdictions, testing blood taken pre-race for TCO2 testing and comparing results between horses who suffered fatal musculoskeletal injuries and competitors from the same races who did not. They examined 21 markers and found three — IGF-1, MMP-2, and IL1RN — which were present in different levels in injured horses versus non-injured horses.

These results made sense to the researchers. IGF-1 is known to play a role in bone development and repair, and it was increased in injured horses, suggesting chronic inflammation was present. Matrix metalloproteinase-2, or MMP-2, is thought to assist with tissue repair and fracture remodeling and was also elevated in injured horses. Interestingly, IL1RN is more commonly known as IRAP–a anti-inflammatory material derived from a horse's own blood and given therapeutically by veterinarians to reduce inflammation and aid in healing an injured horse. IRAP was decreased in fatally injured horses, suggesting the body's natural anti-inflammatory process had been disrupted for some reason. Horses with higher levels of IRAP were actually seven times less likely to suffer fatal injuries.

While those results are encouraging, Page cautioned that it will still be challenging to practically apply the new information. The three biomarkers weren't perfect predictors of impending injury; 24 percent of the time, a horse would not appear to be at risk based on its biomarker levels when in fact it did suffer a fatal injury and 12 percent of the time, tests suggested the horse was at risk of a fatal injury but the horse finished the race without a catastrophic breakdown.

Overall, the three biomarkers provided about 88 percent accuracy at identifying horses at risk.

The test is also expensive and in a research setting the tests took around 48 hours to complete. Page pointed out that those estimates are based on his team's study, where samples had to be tested for 21 different biomarkers. Reducing the number of markers tested would shorten that time, but it would still likely take 24 hours to get results.

Then there's the question of what to do with horses whose blood indicates they may be at risk. It remains unclear whether the commission legally can or should mandate imaging, particularly if the horse doesn't appear lame and no one is sure where the problem might be. Then there's the question of false positive tests — if a horse's entry was contingent upon a biomarker test, horses could be pulled from races who weren't actually at elevated risk, and it would be hard to know which were which.

Commission members acknowledged it will be a challenge to determine how biomarker data could be practically applied to a time sensitive screening process.

Page said he's hopeful the second phase of the study, which looks “upstream” at mRNA responsible for the production of proteins like biomarkers, may provide more specific guidance.

See Page's presentation here:

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A recent study by Sarah Shaffer, Dr. Susan Stover and colleagues at the J.D. Wheat Orthopedic Laboratory at the UC Davis School of Veterinary Medicine sought to characterize bone abnormalities that precede proximal sesamoid bone (PSB) fractures and determine if pre-existing abnormalities are associated with these fractures. The group retrospectively studied cases from California Thoroughbred racehorses that died from PSB fractures, and controls that died for other reasons.

The most common fatal injury in racehorses in the United States, PSB fractures account for 45-50 percent of such injuries in Thoroughbreds, and 37-40 percent in racing Quarter Horses. The PSBs are two comparatively small bones located in the fetlock that act as part of the suspensory apparatus. Fractures in these bones are likely due to the accumulation of repeated, stress-related processes. This is supported by evidence that racehorses in intensive training are at higher risk for PSB fractures, but the exact causes are not well understood.

Other repetitive overuse injuries in horses are known to be bilateral in nature, meaning that they are similar on both sides of the horse, with the more severely affected limb usually incurring the fracture. With this in mind, the study looked at both the fractured PSB and the intact PSB from the opposing limb of the same horse for all of the cases. The researchers hypothesized that horses with PSB fractures would also show evidence of stress in the PSB of the opposite limb and that the bone that sustained the break would show more severe changes than the intact bone.

The results showed that 90 percent of fractured PSBs from the cases had visible discoloration on the surface of the fracture, most commonly (70 percent of the time) in a characteristic crescent pattern. Directly below the cartilage, evidence of bone loss was noted in 70 percent of cases. This bone loss was located in the same region as the discolorations. Fractured PSBs had lower bone volume fraction and tissue mineral density within the lesion sites than comparable locations in opposing limbs and controls. These regions were contiguous with the fracture lines. Evidence of microdamage was also observed in fractured PSBs.

Overall, changes identified in the bones were more numerous in case horses than control horses and more severe in the fractured limbs than the opposing limbs in cases. Sampling from areas of bone distant from the lesions noted no significant differences in bones from case and control horses other than the presence of a lesion.

This data supports the role of microdamage and tissue remodeling in the formation of lesions in PSBs. It is important to note that all of the horses in this study were California racehorses, so it is currently unknown if the results will apply equally to racehorses in other areas. Future studies with larger sample sizes may provide further information.

Understanding the mechanism of PSB fracture is necessary in order to determine risk factors and prevent fractures. Combining this information with advanced technology, such as the recent introduction of positron emission tomography (PET scan) may facilitate identification of horses at risk for PSB fracture and inform management alterations to avoid injury.

* This work was supported with funding from the Grayson Jockey Club Research Foundation, Inc., the UC Davis Center for Equine Health, the Maury Hull Fellowship, and the Louis R. Rowan Fellowship.

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