Phenylbutazone prior to racing and musculoskeletal and fatal injuries

In this well designed study there was a significant increase in the odds (appx 50% greater) of injury, sometimes catastrophic, to racehorses given prerace phenylbutazone. There are several possible reasons but racing horses that are not 100% sound and racing horses on meds that may prevent them from feeling the pain of impending muscoskeletal failure strike me as most likely.
DrO

Association between the administration of phenylbutazone prior to racing and musculoskeletal and fatal injuries in Thoroughbred racehorses in Argentina
J Am Vet Med Assoc. 2020 Sep 15;257(6):642-647.
Authors
Teresita Zambruno, Stamatis P Georgopoulos, Lisa A Boden, Tim D H Parkin

Abstract
Objective: To examine the association between prerace administration of phenylbutazone and the risk of musculoskeletal injury (MSI) and fatal injury in Thoroughbred racehorses that raced between 2006 and 2015 at 2 of the 4 official racetracks in Argentina.

Sample: Data from racetrack databases and veterinary reports on 283,193 race starts.

Procedures: Data were collected relating to race performance and injury outcomes for starts at these tracks. The incidence of MSI and fatal injury was calculated for each year, stratified by the declared prerace administration of phenylbutazone. Univariable logistic regression, followed by multivariable logistic regression, was used to identify significant risk factors for both MSI and fatal injury.

Results: Analyses identified associations between the declared prerace administration of phenylbutazone and the risk of MSI and fatal injury during racing. Horses with declared prerace phenylbutazone administration had greater odds of MSI (OR, 1.45 [95% CI, 1.03 to 2.04]) and fatal injury (OR, 1.59 [95% CI, 1.1 to 2.27]) than did horses racing without prerace phenylbutazone administration. These associations remained significant when other risk factors were accounted for in both multivariable models.

Conclusions and clinical relevance: Results suggested an association between the prerace administration of phenylbutazone and the risk of MSI and fatal injury in Thoroughbred racehorses during racing. Although these results did not imply a direct causal relationship between prerace phenylbutazone administration and injury, they may be considered in the development of more conservative medication policies to optimize racehorse welfare in North and Latin America.