Catastrophic Injuries in Racehorses
Catastrophic musculoskeletal injuries are major causes of death for racehorses, yet their risk factors remain poorly understood and, thus, difficult to manage. Researchers have investigated many potential risk factors in past studies, but it remained unclear whether factors related to the horses’ previous histories of lameness, medication administration, and surgery had any impact on catastrophic injuries. So a team of scientists from the University of Melbourne, in Australia, and the University of California, Davis, conducted a study to find out.

Previously identified risk factors associated with catastrophic musculoskeletal injury or fatality in racehorses include horse age, age at first start, horse sex, race distance, type and condition of track surface, class of race, and number of race starters.

In the current study, Peta Hitchens, PhD, of the University of Melbourne, said the team’s aim was to find modifiable factors associated with horses at risk of catastrophic injury so they can be managed appropriately.

“We surveyed the primary veterinarians of racehorses that had died as a result of injuries sustained during flat racing or training (cases) and of horses that did not die (controls) to determine their history of lameness, medication, and surgery,” Hitchens said.

They studied 146 Thoroughbreds (45 cases and 101 controls) and 17 Quarter Horses (11 cases and 6 controls). All study horses raced or trained in California.

“Thoroughbreds were more likely to have shown signs of lameness before death, especially within the prior three months,” Hitchens said. “But unraced Thoroughbreds were the most likely to have been administered systemic medications. This likely reflects the drug control measures in place in the racing industry, rather than any other causal factor.

“Thoroughbred cases were also more likely to have raced with greater intensity during their whole career, including the three to four months prior to their death, but in the month preceding these cases had eased off,” she added. “We did not find these sorts of significant difference in the Quarter Horses studied, but the sample size for Quarter Horses was small.”

The team found no apparent link between previous surgery and catastrophic injury in either breed, Hitchens said.

The researchers noted inherent difficulties in tracking racehorses’ case histories, which could be improved by detailed veterinary records accompanying horses as they move between stables or training facilities.

“Ideally, complete veterinary records of each horse would be the gold standard for use in analysis; however, until complete veterinary records of all horses are required for regulatory purposes, this approach is not feasible,” Hitchens said.

If horses have been observed to be lame, she said they should be differentially diagnosed when possible to prevent them from resuming high-intensity exercise prematurely.

The study, Relationship Between Historical Lameness, Medication Usage, Surgery, and Exercise With Catastrophic Musculoskeletal Injury in Racehorses,” was published in Frontiers in Veterinary Science.