Epidemiologic analysis of factors influencing exertional rhabdomyolysis inThoroughbreds

Objective-To determine incidence, effect on performance, and management pra ctices associated with exertional rhabdomyolysis (ER) in Thoroughbreds. Sample Population-Medical records for 984 Thoroughbreds and a survey of tra iners of horses with and without ER. Procedures-Medical records for 984 Thoroughbreds stabled at a midwestern ra ce-track were examined to determine the incidence of ER during the 1995 rac ing season. A retrospective questionnaire was administered to trainers to d etermine management practices associated with ER in 59 Thoroughbreds with E R and 47 control Thoroughbreds in training. Multiple logistic regression wa s used to determine management factors associated with ER. Results-ER affected 48 of 984 (4.9%) Thoroughbreds, Two-year-old females we re most frequently affected, and 36 of 96 (37.5%) trainers had greater than or equal to 1 horse with ER, Horses with ER were more likely not to race d uring the racing season, compared with control horses. For horses that race d, differences were not found with respect to racing performance between ER and control horses. Exertional rhambdomyolysis developed frequently in sus ceptible horses that had greater than or equal to 1 day of rest prior to ex ercise and that galloped during exercise. Horses with ER were commonly fed > 4.5 kg of grain daily. Nervous and extremely nervous horses were 5.4 time s more likely, and horses with some form of lameness were 4.2 times more li kely, to have ER. Conclusions and Clinical Relevance-Exertional rhabdomyolysis is common in T horoughbreds, and ER can be affected by temperament, sex, age, diet, exerci se routines, and lameness. Management that minimizes excitability, particul arly when tailored to each horse, may be most effective for controlling ER.