Study Finds Phenylbutazone a Risk Factor in Breakdowns

POSTED ON  |  08-11-2019

Tim Parkin
Based on the groundbreaking results of a recently published study, the epidemiologist who oversees The Jockey Club Equine Injury Database will add phenylbutazone as a risk factor for catastrophic breakdowns and will call for policies that require the non-steroidal anti-inflammatory to be completely clear from a horse's system before it races. In an essay scheduled to be published in an upcoming issue of BloodHorse, Tim Parkin, senior lecturer in clinical epidemiology at the University of Glasgow who has studied the Equine Injury Database for 10 years, recommends the race-day threshold for phenylbutazone be lowered to zero—no tolerance. 

The recommendation, which would be more restrictive than the current policy in every U.S. racing jurisdiction except California, follows a study by one of Parkin's graduate students, Teresita Zambruno, that found a link between phenylbutazone, commonly referred to as bute, and equine injuries—both catastrophic and nonfatal.

Zambruno's study, published online and scheduled for print publication in the Journal of the American Veterinary Medical Association in late 2020, examined data from 500,000 starts at four tracks in South America. While it found some risk factors observed in other studies, it was the first study to find a link between bute and breakdowns.  Zambruno concludes: "This study is the first to clearly demonstrate an association between racing, having recently been administered phenylbutazone, and the risk of fatality. The next challenge is to attempt to turn this information into policy or regulatory change in the racing jurisdictions in which such practices are permitted."

In his upcoming essay for BloodHorse, Parkin says horses racing with bute in their systems are 50% more likely to sustain a fatal or nonfatal musculoskeletal injury than those racing without a recent administration of the non-steroidal anti-inflammatory.  Zambruno's study offered some potential reasons for the increased injury risk of horses administered bute. Those reasons suggest restrictions in the use of bute ahead of timed workouts also could be helpful.

"The increased odds of fatality for the (bute) group is probably because those horses need anti-inflammatories or analgesics to have a good performance or to make it to the race," Zambruno said. "This could be due to clinical or sub-clinical preexisting injuries or pain. Thus phenylbutazone administration may allow horses to continue training and racing, accumulating damage to their musculoskeletal structures and increasing the odds of fatalities due to fatal (injury) during performance."

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