Omneity® Pellets
All-In-One Vitamin & Mineral Pellet
Exertional heat illness: a review of the syndrome affecting racing Thoroughbreds in hot and humid climates.
Abstract: Metabolic heat produced by Thoroughbred racehorses during racing can rapidly elevate core body temperature (1°C/min). When environmental conditions are hot and humid, the normal physiological cooling mechanisms become ineffective. The heat accumulated may exceed a critical thermal maximum (estimated to be 42°C), which may trigger a complex pathophysiological cascade with potentially lethal consequences. This syndrome has been labelled exertional heat illness (EHI). EHI is described in humans, but has not been well documented in Thoroughbred racehorses. The clinical signs described in racehorses would suggest that the pathophysiological events affecting the central nervous (CNS) and gastrointestinal systems are similar to those described in humans. Clinical signs are progressive and include signs of endotoxaemia and increasing levels of CNS dysfunction. Initially, horses that may be mildly irritable (agitated, randomly kicking out) may progress to unmanageable (disorientation, severe ataxia, falling) and ultimately convulsions, coma and death. Currently, the approach to treatment is largely empirical and involves rapid and effective cooling, administration of drugs to provide sedation, administration of non-steroidal anti-inflammatory drugs to ameliorate the effects of endotoxaemia and glucocorticoids to stabilise cell membranes and reduce the effects of inflammation on the CNS. This review provides an overview of the current knowledge about EHI in Thoroughbred racehorses, suggests a likely pathophysiology of the syndrome in horses based on the current literature on heat illness in humans and horses, and outlines current treatment strategies being used to treat racehorses with clinical signs of EHI.
© 2016 Australian Veterinary Association.
Publication Date: 2016-06-29 PubMed ID: 27349884DOI: 10.1111/avj.12454Google 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
- Review
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.
The research article discusses the lethal effects of exertional heat illness (EHI) on racing Thoroughbreds, triggered by the combination of intense physical effort and hot, humid conditions. It provides an understanding of EHI, its progression, and current approaches to treatment based on the existing literature.
Syndrome Overview
- The study focuses on exertional heat illness (EHI), a syndrome affecting racing Thoroughbreds in hot and humid environments. This condition is caused by the rapid elevation of the horse’s body temperature due to intense physical exertion coupled with unfavorable environmental conditions.
- Heat accumulation in horses can reach a crucial threshold of around 42°C, which can trigger a pathophysiological cascade leading to potentially fatal consequences.
- Although EHI is well-documented in humans, information about its effects on Thoroughbred racehorses is limited.
Progression of Clinical Signs
- The research article describes the progression of clinical signs related to EHI affecting the central nervous system (CNS) and gastrointestinal systems of horses, which appear to mirror the underlying physiological changes seen in humans affected by the same condition.
- Early indicators include mild irritability, such as agitation and random kicking. The horse may then progress to unmanageable states involving disorientation, severe uncoordinated movement, and eventually convulsions, coma, and death.
- The clinical signs also include manifestations of endotoxaemia, a condition characterized by the presence of endotoxins in the blood, suggesting systemic infection.
Current Treatment Approaches
- At present, the treatment protocols for EHI in racehorses are primarily empirical, which means they are based on practical experience rather than scientific data or theory.
- The typical treatment approach involves rapid and efficient cooling of the horse to reduce body temperature, administration of sedatives to control agitation and restlessness, administration of non-steroidal anti-inflammatory drugs (NSAIDs) to alleviate the effects of endotoxaemia, and glucocorticoids to stabilize cell membranes and curb the inflammatory effects on the CNS.
Conclusion
- The research article offers a comprehensive overview of EHI in racehorses and suggests the proposed pathophysiology based on the existing literature and understanding of both equine and human heat illness.
- It also provides insights into current treatment strategies, though emphasizing the need for further targeted investigation to improve the prevention, detection, and treatment of EHI in Thoroughbred racehorses.
Cite This Article
APA
Brownlow MA, Dart AJ, Jeffcott LB.
(2016).
Exertional heat illness: a review of the syndrome affecting racing Thoroughbreds in hot and humid climates.
Aust Vet J, 94(7), 240-247.
https://doi.org/10.1111/avj.12454 Publication
Researcher Affiliations
- Barkers Lodge Road, Picton, New South Wales, Australia.
- Research and Clinical Trials Unit, University Veterinary Teaching Hospital Camden, University of Sydney, 410 Werombi Road, Camden, New South Wales, 2570, Australia. andrew.dart@sydney.edu.au.
- Research and Clinical Trials Unit, University Veterinary Teaching Hospital Camden, University of Sydney, 410 Werombi Road, Camden, New South Wales, 2570, Australia.
MeSH Terms
- Animals
- Heat Stress Disorders / etiology
- Heat Stress Disorders / veterinary
- Horse Diseases / etiology
- Horses / physiology
- Hot Temperature / adverse effects
- Physical Exertion / physiology
- Risk Factors
- Syndrome
- Tropical Climate
Citations
This article has been cited 20 times.- Mecocci S, Porzio E, Chiaradia E, Pepe M, Paris A, Bergagna S, Pietrucci D, Chillemi G, Beccati F, Cappelli K. Omic technology to monitoring resilience and adaptation to exercise and heat stress in endurance horses. Front Vet Sci 2025;12:1734969.
- Arfuso F, Rizzo M, Perillo L, Arrigo F, Giudice E, Piccione G, Faggio C, Monteverde V. The Effect of Ambient Temperature, Relative Humidity, and Temperature-Humidity Index on Stress Hormone and Inflammatory Response in Exercising Adult Standardbred Horses. Animals (Basel) 2025 May 15;15(10).
- Ohmura H, Ebisuda Y, Takahashi Y, Mukai K. Effects of pre-exercise cooling in hot environments on performance and physiological responses in Thoroughbred horses. J Equine Sci 2025;36(1):19-23.
- Nielsen SS, Alvarez J, Boklund A, Dippel S, Dorea F, Figuerola J, Herskin M, Miranda Chueca MA, Nannoni E, Nonno R, Riber A, Stahl K, Stegeman JA, Thulke HH, Tuyttens F, Winckler C, Raj M, Velarde A, Candiani D, Van der Stede Y, Michel V. Welfare of horses at slaughter. EFSA J 2025 Jan;23(1):e9178.
- Ebisuda Y, Mukai K, Takahashi Y, Yoshida T, Matsuhashi T, Kawano A, Miyata H, Kuwahara M, Ohmura H. Heat acclimation improves exercise performance in hot conditions and increases heat shock protein 70 and 90 of skeletal muscles in Thoroughbred horses. Physiol Rep 2024 May;12(10):e16083.
- Lampang KN, Isawirodom A, Rungsri P. Correlation and agreement between infrared thermography and a thermometer for equine body temperature measurements. Vet World 2023 Dec;16(12):2464-2470.
- Verdegaal EJMM, Howarth GS, McWhorter TJ, Delesalle CJG. Thermoregulation during Field Exercise in Horses Using Skin Temperature Monitoring. Animals (Basel) 2023 Dec 30;14(1).
- Lisboa BRF, da Silva JAR, da Silva WC, Barbosa AVC, Silva LKX, Lourenço-Júnior JB. Evaluation of thermoregulation of horses (Equus caballus) submitted to two methods of post-exercise cooling, in hot and humid climate conditions, in the Eastern Amazon. Front Vet Sci 2023;10:1150763.
- Kang H, Zsoldos RR, Sole-Guitart A, Narayan E, Cawdell-Smith AJ, Gaughan JB. Heat stress in horses: a literature review. Int J Biometeorol 2023 Jun;67(6):957-973.
- Brownlow M, Mizzi JX. An Overview of Exertional Heat Illness in Thoroughbred Racehorses: Pathophysiology, Diagnosis, and Treatment Rationale. Animals (Basel) 2023 Feb 9;13(4).
- Nielsen SS, Alvarez J, Bicout DJ, Calistri P, Canali E, Drewe JA, Garin-Bastuji B, Gonzales Rojas JL, Gortázar Schmidt C, Michel V, Miranda Chueca MÁ, Padalino B, Pasquali P, Roberts HC, Spoolder H, Stahl K, Velarde A, Viltrop A, Winckler C, Earley B, Edwards S, Faucitano L, Marti S, Miranda de La Lama GC, Costa LN, Thomsen PT, Ashe S, Mur L, Van der Stede Y, Herskin M. Welfare of equidae during transport. EFSA J 2022 Sep;20(9):e07444.
- Verdegaal EJMM, Howarth GS, McWhorter TJ, Delesalle CJG. Is Continuous Monitoring of Skin Surface Temperature a Reliable Proxy to Assess the Thermoregulatory Response in Endurance Horses During Field Exercise?. Front Vet Sci 2022;9:894146.
- Kang H, Zsoldos RR, Skinner JE, Gaughan JB, Mellor VA, Sole-Guitart A. The Use of Percutaneous Thermal Sensing Microchips to Measure Body Temperature in Horses during and after Exercise Using Three Different Cool-Down Methods. Animals (Basel) 2022 May 14;12(10).
- Wang M, Liu Y, Bi X, Ma H, Zeng G, Guo J, Guo M, Ling Y, Zhao C. Genome-Wide Detection of Copy Number Variants in Chinese Indigenous Horse Breeds and Verification of CNV-Overlapped Genes Related to Heat Adaptation of the Jinjiang Horse. Genes (Basel) 2022 Mar 28;13(4).
- Verdegaal EJMM, Howarth GS, McWhorter TJ, Boshuizen B, Franklin SH, Vidal Moreno de Vega C, Jonas SE, Folwell LE, Delesalle CJG. Continuous Monitoring of the Thermoregulatory Response in Endurance Horses and Trotter Horses During Field Exercise: Baselining for Future Hot Weather Studies. Front Physiol 2021;12:708737.
- Gao TY, Yang WC, Zhou FH, Song Q. Analysis of D-dimer cut-off values for overt DIC diagnosis in exertional heat illness. Medicine (Baltimore) 2020 Dec 24;99(52):e23831.
- Kang H, Zsoldos RR, Woldeyohannes SM, Gaughan JB, Sole Guitart A. The Use of Percutaneous Thermal Sensing Microchips for Body Temperature Measurements in Horses Prior to, during and after Treadmill Exercise. Animals (Basel) 2020 Dec 2;10(12).
- Hall EJ, Carter AJ, O'Neill DG. Dogs Don't Die Just in Hot Cars-Exertional Heat-Related Illness (Heatstroke) Is a Greater Threat to UK Dogs. Animals (Basel) 2020 Jul 31;10(8).
- Nomura M, Shiose T, Ishikawa Y, Mizobe F, Sakai S, Kusano K. Prevalence of post-race exertional heat illness in Thoroughbred racehorses and climate conditions at racecourses in Japan. J Equine Sci 2019 Jul;30(2):17-23.
- Lu CX, Qiu T, Liu ZF, Su L, Cheng B. Calcitonin gene-related peptide has protective effect on brain injury induced by heat stroke in rats. Exp Ther Med 2017 Nov;14(5):4935-4941.
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
