Omneity® Pellets
All-In-One Vitamin & Mineral Pellet
Case report: exercise-associated sudden death in a Thoroughbred racehorse with cardiac lesions.
Abstract: Exercise-associated sudden death (EASD), defined as acute collapse and death in an apparently healthy racehorse during or within ~1 h after exercise, is currently among the top concerns in the racing industry. Cases of EASD with no cause of death identified at necropsy are frequently presumed to be of cardiac origin. In such cases, in addition to a regular necropsy, a cardiac examination protocol is performed that includes a detailed gross examination and microscopic evaluation of 11 regions of the heart. Very often this protocol is unrewarding because there are no microscopic lesions to explain the presumed cardiac event. Here we describe the necropsy of a 3-year-old, Thoroughbred gelding that collapsed a few minutes after a workout. The heart was grossly unremarkable, but significant histologic lesions that included multifocal to diffuse cardiomyocyte degeneration and necrosis, lymphoplasmacytic myocarditis, and myocardial fibroplasia were found, particularly in the right and left ventricular free walls and in the interventricular septum. Other lesions included severe pulmonary edema and congestion, splenic congestion, an open castration wound with localized suppurative inflammation and bacteria in the scrotum, and lymphoplasmacytic interstitial nephritis. We believe that the cardiac lesions were severe and extensive enough to have contributed to death. A cause for such lesions was not definitively identified, but it is possible that the infected castration wound predisposed to myocarditis. This case serves as an example of the use of the cardiac examination protocol to map and evaluate lesions in EASD cases.
© 2026. The Author(s).
Publication Date: 2026-07-04 PubMed ID: 42400741PubMed Central: 8965266DOI: 10.1007/s11259-026-11384-0Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Case Reports
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
Overview
- This study reports a case of sudden death in a Thoroughbred racehorse shortly after exercise, where detailed heart tissue examination revealed significant cardiac damage despite no apparent abnormalities during gross examination.
Background
- Exercise-associated sudden death (EASD): Refers to the sudden collapse and death of a seemingly healthy racehorse during or within an hour after exercise.
- Prevalence: EASD remains a major concern in the horse racing industry.
- Common cause assumption: When no obvious cause of death is found at necropsy, cardiac issues are often suspected.
Necropsy and Cardiac Examination Protocol
- In typical cases of suspected cardiac-related death:
- A detailed necropsy is performed.
- The heart undergoes a cardiac examination protocol involving:
- Gross anatomical inspection.
- Microscopic evaluation of 11 specific heart regions.
- However, frequently, no microscopic lesions are uncovered to explain sudden cardiac events.
Case Details
- Subject: 3-year-old Thoroughbred gelding.
- Event: The horse collapsed minutes after a workout and died suddenly.
- Gross heart examination: No visible abnormalities detected.
- Microscopic, histologic findings:
- Multifocal to diffuse cardiomyocyte degeneration and necrosis.
- Lymphoplasmacytic myocarditis (inflammation involving lymphocytes and plasma cells).
- Myocardial fibroplasia (fibrous tissue development in heart muscle).
- Lesions located primarily in right and left ventricular free walls and interventricular septum.
- Other pathological findings:
- Severe pulmonary edema and congestion (fluid accumulation in lungs and blood vessels).
- Splenic congestion.
- Open castration wound with localized pus-forming inflammation and bacterial presence in the scrotum.
- Lymphoplasmacytic interstitial nephritis (inflammatory kidney lesion).
Interpretation and Significance
- The cardiac lesions observed were severe and widespread, and are considered significant contributors to the horse’s sudden death.
- While a definitive cause for the cardiac lesions was not found, the infected castration wound likely played a role in predisposing the horse to myocarditis, suggesting a possible infection-related systemic effect on the heart.
- This highlights the potential link between localized infections and fatal cardiac complications in racehorses.
- The case underscores the value of detailed microscopic examination of heart tissue in unexplained exercise-related deaths, even when no gross abnormalities are seen.
- The cardiac examination protocol used allowed for mapping and assessing the extent of heart damage contributing to EASD.
Conclusions
- Sudden death in racehorses may involve complex and subtle cardiac lesions not evident on gross examination.
- Microscopic heart examinations are crucial for detecting underlying pathology in EASD cases.
- Potential systemic infections should be considered as contributing factors in equine myocarditis and sudden death.
Cite This Article
APA
Acevedo HD, Uzal F, Blea J, Henderson E, Nyaoke A, Schild CO, Asin J.
(2026).
Case report: exercise-associated sudden death in a Thoroughbred racehorse with cardiac lesions.
Vet Res Commun, 50(5), 439.
https://doi.org/10.1007/s11259-026-11384-0 Publication
Researcher Affiliations
- California Animal Health and Food Safety Laboratory System, San Bernardino branch, University of California-Davis, San Bernardino, CA, USA.
- California Animal Health and Food Safety Laboratory System, San Bernardino branch, University of California-Davis, San Bernardino, CA, USA.
- School of Veterinary Medicine, University of California, Davis, CA, USA.
- California Animal Health and Food Safety Laboratory System, San Bernardino branch, University of California-Davis, San Bernardino, CA, USA.
- California Animal Health and Food Safety Laboratory System, San Bernardino branch, University of California-Davis, San Bernardino, CA, USA.
- California Animal Health and Food Safety Laboratory System, San Bernardino branch, University of California-Davis, San Bernardino, CA, USA.
- California Animal Health and Food Safety Laboratory System, San Bernardino branch, University of California-Davis, San Bernardino, CA, USA. jasinros@ucdavis.edu.
MeSH Terms
- Animals
- Horses
- Male
- Horse Diseases / pathology
- Horse Diseases / etiology
- Physical Conditioning, Animal / adverse effects
- Death, Sudden / veterinary
- Death, Sudden / etiology
- Myocardium / pathology
- Death, Sudden, Cardiac / veterinary
- Death, Sudden, Cardiac / etiology
Conflict of Interest Statement
Declarations. Ethics statement: No live animals were used in this report. The described case was submitted for routine necropsy and diagnostic work and no ethical approval is needed. Competing interests: The authors declare no competing interests.
References
This article includes 23 references
- Bennet ED, Parkin TDH. Fifteen risk factors associated with sudden death in Thoroughbred racehorses in North America (2009–2021). J Am Vet Med Assoc 260:1956–1962.
- Boden LA, Anderson GA, Charles JA, Morgan KL, Morton JM, Parkin TD, Slocombe RF, Clarke AF. Risk of fatality and causes of death of Thoroughbred horses associated with racing in Victoria, Australia: 1989–2004. Equine Vet J 38:312–318.
- Buergelt CD. Equine cardiovascular pathology: an overview. Anim Health Res Rev 4:109–129.
- Carrier TK, Estberg L, Stover SM, Gardner IA, Johnson BJ, Read DH, Ardans AA. Association between long periods without high-speed workouts and risk of complete humeral or pelvic fracture in thoroughbred racehorses: 54 cases (1991–1994). J Am Vet Med Assoc 212:1582–1587.
- DeLay J. Postmortem findings in Ontario racehorses. J Vet Diagn Invest 29:2003–2015.
- Diab SS, Poppenga R, Uzal FA. Sudden death in racehorses: postmortem examination protocol. J Vet Diagn Invest 29:442–449.
- Freel KM, Morrison LR, Thompson H, Else RW. Arrhythmogenic right ventricular cardiomyopathy as a cause of unexpected cardiac death in two horses. Vet Rec 166:718–722.
- Gelberg HB, Zachary JF, Everitt JI, Jensen RC, Smetzer DL. Sudden death in training and racing Thoroughbred horses. J Am Vet Med Assoc 187:1354–1356.
- Gunson DE, Sweeney CR, Soma LR. Sudden death attributable to exercise-induced pulmonary hemorrhage in racehorses: nine cases (1981–1983). J Am Vet Med Assoc 193:102–106.
- Hellings IR, Skjerve E, Karlstam E, Valheim M, Ihler CF, Fintl C. Racing-associated fatalities in Norwegian and Swedish harness racehorses: Incidence rates, risk factors, and principal postmortem findings. J Vet Intern Med 36:778–786.
- Johnson BJ, Stover SM, Daft BM, Kinde H, Read DH, Barr BC, Anderson M, Moore J, Woods L, Stoltz J, Blanchard P. Causes of death in racehorses over a 2 year period. Equine Vet J 26:327–330.
- Kiryu K, Nakamura T, Kaneko M, Oikawa M, Yoshihara T. Cardiopathology of sudden cardiac death in the race horse. Heart Vessels Suppl 2:40–46.
- Kiryu K, Machida N, Kashida Y, Yoshihara T, Amada A, Yamamoto T. Pathologic and electrocardiographic findings in sudden cardiac death in racehorses. J Vet Med Sci 61:921–928.
- Lucke VM. Sudden death. Equine Vet J 19:85–86.
- Lyle CH, Uzal FA, McGorum BC, Aida H, Blissitt KJ, Case JT, Charles JT, Gardner I, Horadagoda N, Kusano K, Lam K, Pack JD, Parkin TD, Slocombe RF, Stewart BD, Boden LA. Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings. Equine Vet J 43:324–331.
- Molesan A, Wang M, Sun Q, Pierce V, Desideri R, Palmer S, Todhunter R, Kelly K. Cardiac pathology and genomics of sudden death in racehorses from New York and Maryland racetracks. Vet Pathol 56:576–585.
- Nath L, Stent A, Elliott A, La Gerche A, Franklin S. Risk factors for exercise-associated sudden cardiac death in Thoroughbred racehorses. Animals (Basel) 12:1297.
- Nelke C, Schmid S, Kleefeld F, Schroeter CB, Goebel HH, Hoffmann S, Preuße C, Kölbel H, Meuth SG, Ruck T, Stenzel W. Complement and MHC patterns can provide the diagnostic framework for inflammatory neuromuscular diseases. Acta Neuropathol 12:15.
- Platt H. Sudden and unexpected deaths in horses: a review of 69 cases. Br Vet J 138:417–429.
- Robert MP, Chapuis RJJ, de Fourmestraux C, Geffroy OJ. Complications and risk factors of castration with primary wound closure: Retrospective study in 159 horses. Can Vet J 58:466–471.
- Sikder S, Williams NL, Sorenson AE, Alim MA, Vidgen ME, Moreland NJ, Rush CM, Simpson RS, Govan BL, Norton RE, Cunningham MW, McMillan DJ, Sriprakash KS, Ketheesan N. Group G Streptococcus induces an autoimmune carditis mediated by interleukin 17A and Interferon γ in the Lewis Rat Model of Rheumatic Heart Disease. J Infect Dis 218:324–335.
- Stover SM, Johnson BJ, Daft BM, Read DH, Anderson M, Barr BC, Kinde H, Moore J, Stoltz J, Ardans AA, Pool RR. An association between complete and incomplete stress fractures of the humerus in racehorses. Equine Vet J 24:260–263.
- Uzal F, Asin J, Diab S, Henderson E, Engiles JB, Kennedy L, Schild C. Pathology of sudden death in racehorses: a review. J Vet Diagn Invest .
Citations
This article has been cited 0 times.Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
