Postmortem findings in racehorses from the U.S. Mid-Atlantic region submitted to a Pennsylvania veterinary diagnostic laboratory

We performed a retrospective analysis of postmortem reports for racehorses submitted to the Pennsylvania Animal Diagnostic Laboratory System between July 2017 and July 2025. We included 394 (366 Thoroughbred [TB], 28 Standardbred [SB]) racehorses, 2–11-y-old (median = 4-y-old), from the Mid-Atlantic region. Annually, 34–58 TBs and 1–9 SBs were submitted. TB racehorse submissions were highest in July and October; SB racehorse submissions were highest in June and July. Approximately two-thirds of submitted racehorses died or were euthanized within 1 h of racing or training. Catastrophic musculoskeletal (MSK) injury was the highest reported cause of fatality for both TB (272 of 366; 74%) and SB (15 of 28; 54%) cohorts. In TBs, 245 of 272 (90%) of catastrophic MSK injuries were appendicular skeletal fractures, most involving the forelimb fetlock joints. Fractures of the proximal sesamoid bones predominated, occurring alone or as components of polyostotic fetlock fractures. In SBs, 15 of 15 (100%) catastrophic MSK injuries were appendicular skeletal fractures, most commonly involving the proximal phalanx of hindlimb fetlock joints. Undetermined cause of death was the second highest reported cause of fatalities in both TBs (31 of 366; 8%) and SBs (5 of 28; 18%). Fatalities were rarely the result of non-catastrophic MSK disease or diseases involving other organ systems. Our results are similar to those of published reports from other regions and may help inform research initiatives focused on early disease detection or prevention strategies to reduce the risk of racehorse fatalities and improve equine welfare.