Thoroughbred racehorses who suffer catastrophic musculoskeletal injuries are more likely to show lameness in the three months leading up to their injury than horses that race without incident, research has shown.
A fresh study has focused on Thoroughbred and Quarter Horse racehorses who experienced a catastrophic breakdown during racing or training in California during a year-long period.
The researchers found that horses who were ultimately to suffer a catastrophic breakdown had raced and trained over fewer furlongs in the two months before their injury.
This, they suggest, may have been an indication that horses had been unable to maintain high-exercise intensity without developing lameness before a race.
Peta Hitchens, Ashley Hill and Susan Stover, writing in the journal Frontiers in Veterinary Science, said musculoskeletal injuries were the primary cause of death for racehorses.
In California, there are about two catastrophic musculoskeletal injuries for every 1000 race starts in both Thoroughbred and Quarter Horse racing. This is higher than in countries such as Australia and New Zealand, which have a rate of 0.4 per 1000 starts; and Britain, with a rate of 0.7 per 1000 starts.
The authors noted that California has seen a reduction in the frequency of fatalities, which has been credited to a racing safety program which resulted in horseshoe restrictions, improvements to track surfaces, restrictions on some medications, and education.
They said that while the long list of known risk factors for catastrophic breakdowns among racehorses had been well reviewed, factors related to lameness history, administration of all types of medication, and surgery had yet to be identified.
The researchers set out to detect management factors that increased the risk of catastrophic musculoskeletal breakdowns by comparing medical histories between horses who sustained such injuries, and those who did not.
Racehorse necropsy information was obtained through the California Horse Racing Board Postmortem Program.
Attending veterinarians of Thoroughbreds and Quarter Horses that experienced such injuries were invited to complete an online veterinary medical history survey, as were vets for matched controls.
Survey information was received on 146 Thoroughbreds, comprising 45 injury cases and 101 controls; and 17 Quarter Horses, comprising 11 injury cases and six controls.
Thoroughbred cases were more likely to show signs of lameness within the three months prior to death (37.8%, compared to 23.3% for controls), and were more likely to have been given hyaluronic acid, used for joint inflammation.
The Thoroughbreds who suffered catastrophic breakdowns were also more likely to have raced with greater intensity during their career, but had eased off in the month preceding their fatal injury.
For Quarter Horses, there was insufficient information to detect significant differences between cases and controls that showed signs of lameness, or that were administered medications.
Surgical history was not associated with catastrophic breakdown.
Discussing their findings, the researchers said the reduction in workload among Thoroughbreds heading for a catastrophic breakdown pointed to potential issues in the horses remaining sound.
“Racehorses that have shown signs of lameness in the months preceding their fatal injury are likely to have a pre-existing condition.
“Such pre-existing conditions, stress fractures and/or pathology have been demonstrated in a high proportion of racehorses at postmortem.
“We did not, however, have information on the severity of lameness, or on more specific lameness time-frames closer to the catastrophic musculoskeletal injury occurring.”
They said the information from the study should help to identify high-risk horses more readily.
“Identification of lameness and/or indicators of lameness should be pursued in future studies.”
Hitchins and Stover are with the University of California, Davis; Hill is with the University of Melbourne.
Hitchens PL, Hill AE and Stover SM (2018) Relationship Between Historical Lameness, Medication Usage, Surgery, and Exercise With Catastrophic Musculoskeletal Injury in Racehorses. Front. Vet. Sci. 5:217. doi: 10.3389/fvets.2018.00217