Pathology of sudden death in racehorses: a review

Sudden death (SD) is the second most important syndrome associated with death in racehorses. The cause of SD in a large number of horses remains undetermined, and, in many of these cases, causes are not found by gross or microscopic postmortem examinations. Among the known causes of SD are traumatic injuries, including fractures of skull, neck, and pelvis; intoxications (e.g., anticoagulant rodenticides); and others. For many cases of SD in which no significant lesions are found, heart failure, probably associated with arrhythmias, is suspected. Precise phenotypic characterization of SD in horses is critical for diagnosis and prevention. Standardized gross and microscopic postmortem protocols are needed to discern normal background changes that may be present in healthy horses from significant changes that directly contribute to SD. Here, we review the current knowledge on the pathology of SD in racehorses.