Alcohol and Gaming Commission of Ontario (AGCO) Death Registry / Equine Incidences in Ontario Racing program: 2023 Postmortem summary
Josepha DeLay
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2024;28(2):21.
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 2023 racing season marks the 21st year of the PM program. To date, PMs have been carried out on 1,348 horses, including 634 (47%) Standardbreds, 681 (51%) Thoroughbreds, and 33 (2%) Quarter Horses (Table 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 2023 AGCO PM cases is provided (Fig. 1).
Since 2015, computed tomography (CT) of fractured and contralateral limbs has been carried out 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 2023, CT imaging was performed on 28 limb fracture cases submitted for PM. Pre-existent lesions in bone were identified by CT and considered potentially predisposing to fracture in 14/28 (50%) 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 2023, the cause of death (COD) was investigated in 16/61 (26%) horses that died during or shortly after exercising. Death was attributed to multiple causes including significant pulmonary hemorrhage compatible with the syndrome of equine exercise-associated fatal pulmonary hemorrhage (EAFPH - 7 horses); acute hemorrhage due to various causes (thoracic aortic rupture -1 horse; rib fracture with hemothorax -1 horse; severe hemothorax with source unidentified -1 horse); and skull fracture (1 horse) (Fig. 2). The COD was undetermined in 5/16 (31%) exercise-associated sudden death cases in 2023. Over the duration of the postmortem program (2003-2023), the COD was undetermined in 53/218 (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 the heart as a cause or result of fatal ventricular dysrhythmia, and the diagnosis cannot be confirmed based on PM findings. AHL
Table 1. Breed distribution of AGCO postmortem submissions to the AHL, 2003-2023.
Figure 1. Diagnoses by body system for AGCO postmortem submissions to the AHL, 2023.
Figure 2. Diagnoses by body system for AGCO exercise-associated sudden death cases submitted to the AHL, 2023.
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.