A Hot Topic

A Hot Topic

Fluid and ion losses during exercise and recovery
by Gayle Ecker

The problems encountered by many of the horses competing in the Olympics held in Barcelona underscore the need to improve our understanding of the environmental stress placed on equine athletes during exercise. The next Olympics in 1996 will be held in Atlanta, Georgia, and hot and humid conditions can be expected. It is critical that we continue to develop this area of research in order to help riders and coaches prepare horses to meet these challenges. This is especially true for three-day eventing and endurance horses, however, horses in many disciplines including racing, driving, polo and others will also be affected by the heat and humidity.


Fluid and electrolyte (ion) losses in horses occur in virtually every sport through sweating The sweat losses may be minimal in low duration, low intensity events and easily replaced by the daily diet. However, in events (or training days) requiring high intensity or prolonged duration, sweat rates will be higher and prolonged, resulting in greater total body losses of fluid and ions. It is well established that fluid and ion losses can predispose the horse to many health problems, yet optimal supplementation regimes have yet to be scientifically established. Effective fluid and ion supplementation is aimed at preventing performance problems due to acute losses of fluid and ions and to assist recovery.


A research program to study the fluid and electrolyte losses in horses during exercise of varying duration and intensity has been carried out for three years and field research on endurance horses and the cross-country phase of the Horse Trials have been completed, The underlying goal of this research program is to quantify losses of fluid and ions during exercise and to determine the best methods for prevention and restoration of losses.



Research conducted in the 1991 season on endurance horses showed that current electrolyte supplementation regimes were not maintaining plasma electrolyte and fluid levels. Further field research was conducted at more rides in 1992 and 1993, bringing the total to 12 events, including over 200 horses, covering distance of 30 to 100 miles, over speeds of approximately 6 to 12 mph, and under a variety of weather conditions.


Blood samples and body weights were taken at rest, the midpoint, the finish and one hour after the finish. Blood was analyzed, usually on-site. When possible, samples of electrolyte supplements were analyzed and amounts administered recorded.


Monitoring body weight gives a good indication of total fluid losses during competition, although the results are affected by feeding, urine output and defecation. Average total fluid losses ranged from 2 - 7% of body weight or about 3 - 10% of total body water (for the average 4500 kg horse, this would reflect fluid losses of 9 - 32 L). There could be quite a range in body weight losses, with same horses losing very little to others losing as much as 13% in the same event, despite access to water throughout the ride. The highest losses occurred during rides in the heat or under high intensity conditions (either high speed and/or muddy terrain).


Previous studies have reported that potassium losses from muscle are related to decrements in performance. In our research, it was not uncommon to find horses with low plasma potassium concentrations showing signs of muscle stiffness to varying degrees.


Factors affecting fluid and electrolyte losses

Many factors can influence sweat rates and there fore fluid and ion losses. High temperatures increase the rate of sweating in order for the horse to dissipate heat. High humidity reduces the efficiency of sweat evaporation and in an attempt to dissipate the heat load, horses probably sweat more. Other factors such as distance, speed and intensity may also affect the sweat rage, thus influencing the amounts of fluid and electrolytes needed to replace the losses. Further analysis of these factors in ongoing.


Summary of phase 1 of the research
Phase one of the research, the field work conducted over two summers on over 200 horses to quantify losses occurring under competitive conditions, is now basically complete. The conclusions of this phase, which were presented at the Focus on Endurance seminars, are:
1. Current supplementation regimes are not adequate for maintaining body water and plasma volume.
2. Current supplementation regimes are not adequate for maintaining whole body and plasma ion concentrations for most horses.
3. Increases in distance, speed (intensity), temperature and adverse terrain may interact to contribute to increased losses of fluids and ions. The effects on ions are varied.
4. Educational efforts are necessary and implementation of these improvements as part of training programs will help participants at all levels.
5. Guidelines for improved supplementation will help to avoid/minimize fluid and ion losses in order to optimize performance, enhance recovery, and prevent the associated problems. The development of effective guidelines for supplementation awaits lab research.


b) Young riders and horse trials

In consolation with Mr. John Neil, coach of the Young riders, research was under taken to study the fluid and ion losses occurring in horses during the cross-country phase (duration of approximately 6 minutes with 12 - 24 obstacles and speeds of 400 - 555 m/min.) of the Ontario Horse Trials. Blood samples and body weights were taken at rest, before the cross-country event, at the finish and 30 minutes after the finish.


The research was carried out at Horse Trials held at Grandview Equestrian Centre in Hawkstone, Ontario on three different occasions. About eight to 10 horses competing in Young Riders, Preliminary, and Intermediate divisions were included at each event. The third event was very muddy whereas the footing for the first two was firm. Due to the cross-country phase, horses lost between 4 and 10 L of fluid which represents body weight losses between 1 - 3%. After Grandview 1 and 2, most of the fluid was regained within 30 minutes, probably due to water consumption. In Grandview 3, losses of 5 - 15% of water and ions occurred despite cool environmental conditions with little recovery of ions before stadium jumping. Total body water had not been restored by 30 minutes, possibly because of higher sweat losses due to the added intensity caused by the muddy conditions. There were several horses which arrived on the site with varying degrees of dehydration due to trailering, and these fluid levels may not have been restored before the event in some horses. Efforts must be made by riders to encourage adequate fluid consumption before the start of the event and during the 30 minutes post-finish to ensure optimal recovery.


This research showed that losses of fluids and ions can be measured under field conditions, with minimal disturbance to preparation by the riders. The losses of fluid and ions during the cross-country phase of the Horse Trials were small due to the short duration of the course and moderate temperatures. Given conditions of heat and humidity and greater duration, however, the losses could be anticipated to be of greater magnitude and at levels which may impair performance.


Lactate levels following the event and recovery suggested that while some horses were adequately trained for the event and rated effectively over the course, other horses would benefit from additional conditioning before competing. When the horse is not conditioned enough for the stress of the event, the chance of injury during the cross-country course, and subsequently in the stadium jumping, would be increased with the ensuing fatigue.


Implications for three-day eventing

The cross-country phase is an important part of three-day eventing and, due to the high intensity and prolonged duration, may result in significant losses of fluid and ions. With the Olympics in Atlanta, Georgia in 1996, the concern for proper training and heat acclimatization of horses is growing. Horses performing in heat and humidity will have added stress during and following the event. With research into this area, we will gain important knowledge on acclimating horses to perform under conditions of heat and humidity, with an aim to reduce the health risk and prevent related problems.


Research into the area of heat stress and acclimation to heat will enable the development of improved guidelines for effective heat acclimation and fluid and electrolyte supplementation before, during and following the event to enhance recovery and replenish losses.


Future research

Phase two of the research plan will look at the fluid and ion losses during controlled conditions on the treadmill. Speed, distance, intensity and environment factors can be controlled in the laboratory and the losses accurately quantified. The mechanisms that allow a horse to acclimate to exercise in the heat will be investigated by conducting field research and on the treadmill. Various electrolyte supplements can also be tested on the horse while at rest, during exercise and recovery in order to determine effective methods of restoring these losses. The results of this research will be of benefit to many sectors of the equine industry, wherever horses may be required to exercise in hot and humid conditions.



The contents are copyrighted but may be copied,
on condition that the Equine Research Centre be
acknowledged for the use of its information.

The Equine Research Centre
University of Guelph
Guelph, ON N1G 2W

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