Study Finds Statistical Relationship Between Pre-Race Bute And Injury In South American Runners

by | 12.03.2019 | 1:46pm

A study that will be published in an upcoming issue of the peer-reviewed Journal of the American Veterinary Medical Association (JAVMA) has found a statistical relationship between pre-race phenylbutazone administration and the risk of injury or breakdown in South American racehorses. 

Research conducted by Dr. Teresita Zambruno at the University of Glasgow examined 500,000 starts in Latin America, comparing a range of variables with the runners' risk of injury or fatality. Researchers believe Zambruno's work is the first study to show a connection between medication regulation and injury risk. 

Multivariable modeling used in the data analysis allowed Zambruno to isolate one risk factor (like medication status) from age, gender, racing class and other demographics to pinpoint how much change in risk level could be attributed to that one factor. When other factors were filtered out, the risk of injury went up 45 percent in horses on pre-race bute compared to those not getting pre-race bute; the risk of fatal injury went up 59 percent. 

When it comes to applying this data to North American runners, however, it's difficult to make a one-to-one comparison because the regulations surrounding pre-race bute in South America are quite different. During the study period, bute was prohibited in horses younger than four and any horses in black type races at the unidentified tracks where data was collected. 

“Each trainer must declare if they are giving bute to the horse to run before the meeting starts. What is uncertain is the time, the day and the dose that is given to the horse,” said epidemiologist Dr. Tim Parkin, who oversaw Zambruno's research while she was a PhD candidate. “We know many people give it the day of the race and a couple of days before. Some of them give it for several days up to the day before racing. Some others use it to train and declare it in case it is not withdrawn yet.

“Honestly it depends on the trainer and private veterinarians' criteria, since it is not administered by official vets.”

Parkin said the research team does not believe the cause of the increased fatality risk is the chemical structure of phenylbutazone impacting a horse's skeleton in some way. Rather, they suspect the association is present because a horse getting pre-race bute is more likely to have some chronic, possibly undetected, underlying damage, injury or soreness for which the medication is compensating. A horse continuing to run on subclinical damage may be making that damage worse.

In an upcoming essay in The Blood-Horse, Parkin is expected to call for new restrictions on pre-race bute usage in North American racing that would require the drug to completely clear a horse's system before a race. Parkin is the lead epidemiologist responsible for analyzing data submitted to the American Equine Injury Database.

Currently, the ARCI Controlled Therapeutic Medication Schedule recommends bute be withdrawn 24 hours prior to race time.

Zambruno's research also looked at a number of other potential risk factors. She found that older, male, heavier horses were more likely to experience injury. The odds of injury increased by 5 to 13 percent for every extra 10 kilograms of the horse's body weight. She also noted that anabolic steroids, although forbidden in South America at the time of her research, were not well-detected in post-race testing at the time and may have had an influence on a horse's weight.

Data from each of the four tracks studied showed that increasing age raised a horse's risk of injury, although the age at which the risk began to grow varied by track. Males had between a 20 and 30 percent higher chance of injury than females, possibly because females were more likely to be retired earlier to begin breeding careers.

Parkin said that in the upcoming JAVMA paper, the team also examines the influence of furosemide (Lasix) on injury risk. (The studied racetracks began placing restrictions on furosemide in 2014, prohibiting it from use in Group 1 and 2 races, and the following year banning it in all group and listed races.)

Parkin said there was no statistical connection observed between furosemide use and injury in this study.

Overall risk of musculoskeletal injury (fatal and non-fatal) varied between the four South American racetracks studied from 1.33 per 1,000 starts to 2.16 per 1,000 starts, with an average of 1.82 per 1,000 starts. 

The Equine Injury Database (EID), which measures fatal injuries in the United States, has ranged from 1.54 to 2 per 1,000 starts. Last year's figure was 1.68. Although many of the deaths reported to the EID are musculoskeletal, the database includes deaths from other causes as well.

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