THE Covid-19-delayed Tokyo Olympics will take place in the heat and humidity of the Japanese summer this year, in temperatures likely to reach more than 41°C.

The Equine Veterinary Journal (EVJ) has put together a Special Collection of previously published articles covering the health and welfare of horses competing in hot and humid conditions. These articles are free to access and it is hoped they will help involved vets keep equine athletes safe in the extreme heat that is expected in Tokyo this summer.

This is not the first time the Olympic Games have taken place in great heat and humidity. Following the 1992 Barcelona Olympics, which saw horses struggling to cope with the heat during the cross country phase of the eventing competition, revolutionary research was carried out to ensure the safety and welfare of horses in the following 1996 Games in Atlanta.

The special collection explores:

  • Physiological, metabolic and biochemical responses of horses competing in the speed and endurance phase of a CCI4* three-day-event
  • Physiological responses to the endurance test of a three-day-event during hot and cool weather
  • Physiological responses of horses competing at a modified 1* three-day-event
  • Adaptations to daily exercise in hot and humid ambient conditions in trained thoroughbred horses
  • Sweating rate and sweat composition during exercise and recovery in ambient heat and humidity
  • Physiological responses of horses to a treadmill simulated speed and endurance test in high heat and humidity before and after humid heat acclimation
  • Comparison between two post-exercise cooling methods
  • Contributions of equine exercise physiology research to the success of the 1996 equestrian Olympic Games
  • An index of the environmental thermal load imposed on exercising horses and riders by hot weather conditions
  • Use of the Wet Bulb Globe Temperature (WBGT) index to quantify environmental heat loads during three-day-event competitions
  • Risk factors for exertional heat illness in thoroughbred racehorses in flat races in Japan

    • In addition to these 11 research papers, FEI veterinary surgeon Christopher Elliott provided a comprehensive editorial forward which highlights the importance of ensuring the health and welfare of equine athletes in the face of heat and humidity.

    This editorial gives an insight into what the Games will look like for equine athletes, how humans can prepare horses for the challenges they will face and how the research from the Special Collection will allow team vets care for horses at this year’s Games.

    Managing equine athletes in hot and humid conditions

    THE Olympic equestrian disciplines of eventing, jumping and dressage made their Olympic debut in Paris 1900 but were absent in 1904 and 1908 before returning in 1912.

    Equestrian has been a permanent feature of every Olympic Games since. A variety of complex and often controversial factors contribute to the selection of future Olympic Games host cities. Unfortunately, climatic challenges and suitability to successfully host equestrian events appears to rarely rate a mention.

    Tokyo certainly is not the first time that extreme heat and humidity has challenged the viability of equestrian events at the Olympic Games, and it won’t be the last. In the face of global climate change and future Olympics, host cities including Paris 2024 and Los Angeles 2028, both of which regularly experience hazardous heatwaves each summer, managing equine athletes in hot and humid conditions will be something veterinarians will be challenged with for many years to come.

    Revolutionary research

    The research carried out post-1992 Barcelona Olympics revolutionised our understanding of managing equine athletes in hot and humid conditions and allowed the successful running of the 1996 Atlanta Olympics.

    It was the 1992 Barcelona Olympic Games that brought the challenges of managing equine athletes in hot climates to the fore of the minds of the International Olympic Committee (IOC), the Federation Equestrian International (FEI), and veterinarians alike.

    Live TV coverage of distressed horses during the cross-country phase drew sharp focus and concern. Veterinarians working on cross-country that day reported many horses finishing with rectal temperatures of at least 42°C, which was the highest reading capacity of thermometers available at the time.

    A commonly held belief at the time of the 1992 Games was that it is beneficial for horses to avoid training in the heat of the day so as to avoid getting too hot. A lack of understanding of acclimatisation combined with inadequate post-exercise cooling techniques and a competition schedule that did not consider climatic factors thoroughly enough are thought to have been major contributors to the events that transpired on cross-country day.

    Following the 1992 Games, and in advance of the predicted extreme climatic conditions of the 1996 Atlanta Olympic Games, an initiative launched by the FEI led to a huge amount of scientific progress in the veterinary understanding of the effects of exercising horses in hot and humid conditions, optimal methods of cooling horses and equine athlete acclimatisation.

    Limited knowledge

    Prior to this initiative, the knowledge in this field was very limited, with only about 20 articles published between 1960 and 1992. More than 20 articles were published in just three years from 1993 to 1996, and this foundational work led to better understanding of the field, improved welfare and performance of equine athletes and great advances in more recent times.

    The concerted effort made during this time led to the establishment of appropriate methods for monitoring and cooling down horses post exercise, recognition of tired horses, identification and management of horses affected by heat stress, modification of competition schedule and length of cross country course when faced with challenging climate and best practice protocols for heat acclimatisation of equine athletes; all of which are now widely accepted and commonplace but at the time lacked scientific evidence to challenge established dogma.

    Research was focused around the cross country phase of eventing as it is the most physically demanding aspect of all the Olympic equestrian disciplines.

    Studies utilising treadmills and standardised exercises testing were able to thoroughly investigate the clinical and physiological effects of exercise in both cool and hot/humid climates.

    These studies demonstrated exercising in hot/humid environments not only increased clinical parameters such as heart rate and respiratory rate, and biochemical markers such as lactate, but one also showed reduced performance markers as shorter mean run times to fatigue.

    Weight loss and sweating rate in cool conditions compared to hot/humid conditions were investigated in several studies by different authors. One such study clearly demonstrated increased sweating rate and increased weight loss in horses exercising in hot/humid conditions compared to the cool.

    These findings led to the recommendation at the 1996 Atlanta Olympics for horses to be weighed twice daily with forced rehydration via either nasogastric tube or intravenous perfusion instituted when horses approached 5% total progressive body weight loss.

    Acclimatisation

    The lack of knowledge regarding heat acclimatisation was a contributing factor in the difficulties encountered at the 1992 Games and was a key focus of research leading into the Atlanta Games. All studies on this topic showed a significant benefit of heat acclimatisation across numerous parameters.

    Studies prior to 1996 indicated daily exposure for three weeks to heat and humidity resulted in physiological adaptions and heat tolerance. This led to the requirement that horses competing at the 1996 Games arrive on site in Atlanta three weeks prior to the competition.

    Subsequent to this, more recent work into acclimatisation has demonstrated that a 15-day period of training in hot humid conditions is adequate to achieve acclimatisation. As years have progressed, the demands of modern equestrian sport have changed. The elimination of roads and tracks within eventing has reduced the physical demand of the horse, but with an increased frequency of competitions along with higher financial risk-reward demand, pressure on horses has increased in other ways.

    Horse arrivals prior to the Olympics are now scheduled approximately seven days prior to competition. Active acclimatisation strategies are instituted for several weeks at home prior to departure. These strategies include training during the hottest part of the day and exercising on treadmills in heated rooms. Comprehensive veterinary advice regarding heat management and acclimatisation is communicated to national equestrian federations well in advance of the games via the FEI.

    Many misconceptions regarding the most appropriate way to cool down horses after exercise were prevalent and persistent prior to the 1992 Games.

    Understanding the importance of this, numerous research projects leading into the 1996 Games clearly showed aggressively cooling with water reduced rectal temperature, heart rate, pulmonary artery temperature and gluteal temperature with no adverse effect on muscle derived enzyme.

    Based on this research, cooling techniques such as misting tents and access to high volumes of cool water at the end of cross country were put in place and deemed successful in a veterinary review of the 1996 Games.

    Study in this topic has been ongoing with the most recent work being from a Japanese research team who compared five different techniques to cool down horses. Using horses exercising on a treadmill in a hot/humid environment, it was shown that continuous application of large volumes of tap water to a stationary horse was the most effective method of reducing core temperature post exercise when compared to walking with no additional cooling, walking with a fan being applied or walking with intermittent application of cold water with or without scraping.

    Early morning starts for cross country and better cooling facilities are now standard wherever hot and humid climate challenges are present. Recommendations regarding active acclimatisation strategies have been perfected and a highly effective system for rapid cooling systems utilising shade tents, misting fans and large volumes of readily available cold water established.

    The protocols, guidelines, techniques and technologies established at the 2008 Games are now used widely and provide the base for veterinary management of all subsequent Olympics. The work done leading into the 2008 Games has been replicated and expanded on leading into Tokyo with a similar method of pre-Olympic climatic modelling in order to provide specific veterinary heat management plans and protocols.

    Prevention is always better than cure, but when presented with a horse experiencing heat stress, it is essential that rapid recognition, treatment and management are instituted.

    The challenging climatic conditions of the delayed 2020 Tokyo Olympic Games are fast upon us. We must consider history and, as veterinarians involved in the management of athletic horses competing in hot and humid climates, must understand the core research that forms the base of our current understanding and ensure we heed the lessons learnt by our predecessors. This is vital to ensure the safe and successful completion of the equestrian events of the 32nd Olympiad in Tokyo.