Term Paper: Animals Thermoregulation

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[. . .] However, this balance is not maintained, and a horse's sweat is more concentrated in electrolytes. If there is not a minimum electrolyte replacement, a horse can suffer from ailments such as kidney impairment, cardiac arrhythmias, and poor tissue perfusion.

Heat Exhaustion and Olympic Horses

In 1992, at the Barcelona Olympic games, several horses suffered from heat exhaustion, which lead to concern about the welfare of the horses at the 1996 Atlanta games, due to the hot and humid climate. While there were talks about modifying or canceling the equestrian events, the Animal Health Trust in Newmarket, England set up a project in order to make recommendations on transport, acclimatization periods and modifications to the competition to ensure that horses were not placed under unnecessary stress. Prior to departure, all countries competing were circulated with detailed recommendations relating to preparation (including diet, training, cooling and pre-acclimatization), transport and subsequent acclimatization in the U.S.A. There was also additional advice on management of horses and riders before, during and after competition (e.g. rehydration, cooling, etc.).

The effectiveness of these measure was to a large extent dependent on acceptance, interpretation and implementation by individual teams and was therefore essentially optional. There were other measures implemented to ensure the welfare of the animals including air-conditioning of the Atlanta quarantine station, well ventilated stables, portable shade from mesh screens, fans and a large covered warm-up area. The Three-Day Event had changes made to its format including an earlier starting time, a reduced distance, cooling stops on the second roads and tracks and an extended '10 minute box' to allow more time for cooling and monitoring the horses.

Decreased Exercise Capacity

A research team for the Atlanta Olympics found horses have a marked reduction in exercise capacity in extreme heat and the optimum acclimatization period is 10 to 14 days. The team made this determination after exposing thoroughbred horses to high heat and humidity and then measuring various physiological responses. The main criterion was how fast the body temperature increased, and if it was slower at the end of three weeks, it was indicative of better heat dissipation.

The researchers also compared acclimatization responses in horses and humans to determine if they were similar. They found that after 20 days of acclimatization, humans have an increased exercise capability through an integrated series of physiological responses. Horses and humans are the only mammals that primarily use sweating as a cooling mechanism, and while horses sweat at two to three times the human rate, they have less surface area over which to lose it.

Three Weeks of Acclimatization

It was recommended that horses participating in the 1996 Olympic games spend three weeks in Georgia prior to competition in order to acclimate to the hot temperatures and high humidity of the region. The horses were fed grain and fat, which have a lower heat increment than fibrous feeds such as hays, to assist them in the hot climate.

The efforts were rewarded by only minor, non-heat related problems with horses competing in the Dressage and Show Jumping competitions, with no cases of anhydrosis (loss of sweating). Two-thirds of the horses which started the Three-Day Event Speed and Endurance test finished in both team and individual competitions, which is considered normal. Examination of the body temperatures of horses throughout the day showed that horses that started early, finished with very similar temperatures to those that went late, providing good evidence that the effects of the climate on the horses had been greatly reduced.

Cold Water Cooling

Cold water cooling is a method that, if it is applied correctly, can cool down hot horses rapidly after competing, thus speeding recovery times and reducing the chances of heat stress. Horses that are hot (above 40 degrees C) and competing in hot environments (above 26 degree C) and are cooled quickly during or after competition, are less likely to suffer heat stress, will recover more quickly, will not become as dehydrated and are almost certain to perform better.

The cold water cooling technique cools horses using two of the three ways they normally lose heat- convection and evaporation. The technique is started as soon the horse finishes exercising, while taking the animal's rectal temperature. Cold water is applied to the horse, with special attention to the large muscles in the quarters, which get extremely hot during movement. It is crucial to continuously apply water to the animal for 20-30 second periods, and then walk the horse for 20-30 seconds in order to promote blood flow to the skin and cooling by convection, as the air movement aids cooling by evaporation. The rectal temperature should be periodically taken, and should fall about 1 degree C. In 10 minutes. It is important to provide the horse with water during exercise in order to help with the cool down process and reduce the effects of dehydration. The process should be stopped if the rectal temperature is less than 38-39 degrees C, the skin over the quarters is cool to touch after a walking period, the respiratory rate is less than 30 breaths per minute and if the horse shivers continuously. It is important to concentrate on cooling as much of the body surface as possible with cold.

Preventative Care

There are other things which should be considered when exercising a horse. A horse should not have an excessive amount of grease applied to its body prior to a cross-country event, since grease acts as insulation, limits or prevents sweating, and limits sweat evaporation. A horse should not be allowed to stand still for prolonged periods. Since water is rapidly expelled from the stomach, the horse should be allowed to drink small amounts of water during competition, and water should be left in the stable until 15-30 minutes before exercise. Muscles work more effectively when they are warm, so horses need to be warmed up prior to exercise. While a moderate increase in body temperature is not harmful, a horse will warm up faster in hot weather.

A horse must be properly cooled-down following exercise work-outs, and because the built up heat must be removed through respiration and sweat, air flow is vital. Walking a hot horse allows the air movement to continue to help evaporate heat, but if the horse is left standing still, the lack of air movement could force the internal temperature to rise higher.

Important Statistics

When a horse is engaged in exercise, only about 25% of the energy used in the horse's working muscles is converted to actual muscle movement, while the remaining 75% is represented by waste heat that becomes very difficult for the horse to dissipate in hot and humid weather.

While radiation of heat from a horse's body into the atmosphere is a potential mode of heat dissipation, it most often works in the opposite direction during sunny days, with horses

(especially dark ones) gaining radiant heat from the environment.

The single most effective means a horse has for getting rid of the enormous heat load generated during exercise is evaporation, accounting for 65% of the heat dissipation, with the lungs accounting for about another 25%.

"While horses have a sweating capacity that is almost double that of humans, the low surface area-to-mass ratio of the species imposes great demands on the thermoregulatory system during moderately intense exercise. Selective brain cooling occurs in the nasal cavity of the horse and serves to cool venous blood. When a horse sweats, the temperature declines by 2.5 C,

and dissipates 60% of total heat produced (McConaghy 1994)."

Conclusion

Thermoregulation is essential for a mammal to survive in extreme hot and cold conditions. Horses and humans are the only mammals which sweat to control body temperature, and understanding thermoregulation is extremely important when it comes to exercising and cooling down horses in various climates.

Bibliography

Andersson, BE. (1984). "Temperature regulation and environmental physiology," in: Dukes'

Physiology of Domestic Animals, Dukes, HH (ed.), Comstock Pub. Associates, Ithaca,

New York.

Austin, H. And Sillence, M. (2004). "Animal physiology: study guide," Charles Sturt University,

Wagga Wagga, NSW.

Causey, G and Whittow (eds). (1973). Comparative Physiology of Thermoregulation, Vol. 1-3,

Academic Press, New York.

Clayton, H. (1991). "Thermoregulation in Conditioning Sport Horses." Sport Horse, Saskatoon.

pp. 61-70.

Cunningham, JG (ed.). (2002). "Thermoregulation," in: Textbook of Veterinary Physiology, 3rd

Ed., Saunders, Philadelphia, Pennsylvania.

Geor, RJ, and McCutcheon, LJ (1996). "Thermoregulation and clinical disorders associated with exercise and heat stress," Compendium on continuing education for the practicing

Veterinarian 18 (4): 436 & APR.

1. Hodgson, Dr., McCuteon, LJ, Byrd, SK, et al. (1993). "Dissipation of metabolic heat in the horse during exercise." Journal of Applied Physiology 74 (3): pp. 1161-1170. MAR.

2. McConaghy, FF, Hales, JRS, Rose, RJ, et all. (1995). "Selective brain cooling in the horse during exercise and environmental heat stress." Journal of Applied Physiology 79 (6):

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