Alcohol and Gaming Commission of Ontario (AGCO) Death Registry / Equine Incidences in Ontario Racing program: 2024 Postmortem Summary
The Alcohol and Gaming Commission of Ontario (AGCO; formerly the Ontario Racing Commission, ORC) continues in its proactive approach to advance racehorse welfare and safety of human and animal participants. In 2003, Ontario became one of the first North American racing jurisdictions to require mandatory reporting of racehorse deaths, in order to monitor, research and improve knowledge of why these events occur. Postmortem (PM) exams conducted at the Animal Health Laboratory (AHL) through the AGCO Death Registry (DR, 2003-2016) and Equine Incidences in Ontario Racing (EIOR, 2016-current) programs continue to provide comprehensive data regarding the causes of morbidity and mortality in racehorses in this province.
The 2024 racing season marks the 23rd year of the PM program. As of December 31, 2024, PM has been carried out on 1,416 horses, including 661 (47%) Standardbreds, 721 (51%) Thoroughbreds, and 34 (2%) Quarter Horses (Fig.1). Annual variation in the number of PM cases reflects the discretionary requirement for PM of reported deaths on the part of the Registrar of AGCO.
A summary of diagnoses by body system for 2024 AGCO PM cases is provided in (Fig. 2).
Since 2015, computed tomography (CT) of fractured and contralateral limbs has been performed on select AGCO postmortem cases through collaboration with the Diagnostic Imaging section of the Ontario Veterinary College Health Sciences Center. The goal of this in-depth examination is to identify pre-existent lesions, primarily in bone, that contribute to catastrophic fractures. In 2024, CT imaging was carried out on 39 limb fracture cases submitted for PM. Pre-existent lesions in bone were identified by CT and considered potentially predisposing to fracture in 22/39 (56%) cases.
Exercise-associated sudden death continues to be of concern to the racing industry. At the AHL, an in-depth PM protocol is used in the evaluation of these cases, with special emphasis on cardiovascular and respiratory systems. In 2024, the cause of death (COD) was investigated in 8/68 (12%) horses that died during or shortly after exercising (Fig. 3). Death was attributed to significant acute pulmonary hemorrhage compatible with the syndrome of equine exercise-associated fatal pulmonary hemorrhage (EAFPH) in 3 horses; significant hemorrhage at other anatomic sites in 3 horses (aortic rupture and hemothorax -1 horse; hemoperitoneum -1 horse; dissecting subaortic hemorrhage – 1 horse); and to pericarditis and myocarditis in 1 horse. The COD was undetermined in 1 horse. Over the duration of the postmortem program (2003-2024), the COD was undetermined in 54/226 (24%) sudden death cases. It has been speculated that exercise-associated cardiac dysrhythmia, leading to acute heart failure and pulmonary hypertension, may be the underlying cause of death among many of these horses, and may also contribute to pulmonary hemorrhage. Typically, no morphologic lesions are detected in heart to explain the cause of speculative fatal ventricular dysrhythmia, and the diagnosis cannot be confirmed based on PM findings.
Figure 1. Breed distribution of AGCO postmortem submissions to the AHL, 2003-2024.
Figure 2. Diagnoses by body system for AGCO postmortem submissions to the AHL, 2024.
Figure 3. Diagnoses by body system for AGCO exercise-associated sudden death cases submitted to the AHL, 2024.
References
1. DeLay J. Postmortem findings in Ontario racehorses, 2003-2015. J Vet Diagn Invest 2017;29(4):457-464.
2. Molesan A, et al. Cardiac pathology and genomics of sudden death in racehorses from New York and Maryland racetracks. Vet Pathol 2019;56:576-585.
3. Physick-Sheard PW, McGurrin MKJ. Ventricular arrhythmias during race recovery in Standardbred racehorses and associations with autonomic activity. J Vet Intern Med 2010;24:1158-1166.
4. Rocchigiani G, et al. Pulmonary bleeding in racehorses: A gross, histologic, and ultrastructural comparison of exercise-induced pulmonary hemorrhage and exercise-associated fatal pulmonary hemorrhage. Vet Pathol 2022;59:973-982.
5. Stover SM. Nomenclature, classification, and documentation of catastrophic fractures and associated pre-existing injuries in racehorses. J Vet Diagn Invest 2017;29:396-404.