Poster Presentation 24th International Conference of Racing Analysts and Veterinarians 2026

Exercise associated sudden death at Horseracing Safety & Integrity Authority covered racetracks July 1 2022 through June 29 2025 (130177)

Karen A Hassan 1 , Susan M Stover 2 , Donovan L Dearmin 3
  1. Compliance and Research, Horseracing Integrity and Safety Authority, Lexington, Kentucky, United States
  2. Surgical & Radiological Sciences, UC Davis School of Veterinary Medicine, Davis, California, United States
  3. Economics, Business and Finance, Lake Forest College, Lake Forest , Illinois, United States

Background: Exercise associated sudden death (EASD) accounts for 13-25% of Thoroughbred racehorse fatalities. Identification of risk factors could aid EASD prevention.

Objective: To describe EASD cases reported to the Horseracing Integrity & Safety Authority (HISA) July 1, 2022 through June 29, 2025 and compare lifetime past performances with those of matched control horses.

Methods: Retrospective analysis of HISA database was performed. Lifetime past performance records were compared between EASD cases and 3 last event matched controls using ANOVA and Kruskal-Wallis tests.

Results: 192 EASD horses (43.2% gelding, 38.5% female, 16.7% intact male, 1.6% ridgling; 17.7% 2-year-old, 25.0% 3-year-old, 24.% 4-year-old, 14.6% 5-year-old, 11.5% 6-year-old, 6.3% >6-year-old) were identified among 85,173 HISA covered racehorses. Necropsy findings were inconclusive in 54%, suspected EIPH in 18%, and only 8% non-cardiorespiratory.

Training EASD (127, 66%) were more common than racing EASD (65, 34%). Most horses (35%) had five or less starts and 12% had no starts. For known pace, training EASD (95) occurred while breezing (59%), galloping (34%), or jogging (7%). Racing EASD (65) occurred most commonly in claiming races (37%) followed by maiden special weight (18%), and allowance optional claiming (14%).

EASD horses were exercised at high speed less often and for shorter distances than controls: on average, 1.5 and 2 fewer furlongs in the last 1 and 2 months, respectively, and when active had 3 fewer works and events per year, with 9 fewer work furlongs per month and 2 more days between works (p-values <0.001 to 0.023).

Discussion: Thoroughbred racehorses experienced EASD early in their career and most commonly in training. EASD horses are exercised less intensely than matched controls. Necropsy findings were nondefinitive, supporting the supposition that EASD is a result of cardiac arrhythmia. Focusing efforts on evaluation of horses during training early in their careers may help prevent EASD.

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