Page 95 - August_2023

Panting is a far less‐effective heat dissipation mechanism than sweat; however, panting can eliminate as much as 15% of the heat load.
A horse sporting a full hair coat is at risk of over‐ heating since hair insulates against heat dissipation.
training ingredient is essential to the success and well-being of any athletic horse: Fitness of the cardiovascular system. As muscles train to better efficiency, less work is needed to achieve a certain level of athletics, with less heat generated by the body.
Fitness and good circulation are essential for efficient heat dissipation. Cardiovascular recovery is only one of many parameters
used to evaluate metabolic well-being and to monitor how efficiently a horse responds to athletic demands. In hot and humid weather, sweat is not always enough to stay ahead of heat build-up. Heart rate and respiratory rate may remain elevated for a short period once exercise stops. Blood flow coursing through his body flushes the bulk of heat to the skin for evaporative cooling, while respiration serves a minor role in cooling.
As internal body temperature rises, sweat is not the only means a horse can use to dissipate heat. Respiration may remain elevated, with nostrils flared as a horse gulps the air. His flanks move rapidly in and out with each breath, giving the impression that he is “panting.” Panting is
a far less-effective heat dissipation mechanism than sweat; however, panting can eliminate as much as 15% of the heat load. The dynamic
of rapid breathing in a horse is similar to what happens as a panting dog moves air across his hanging tongue. Warmed blood flowing from heated skeletal muscles circulates to the heart and through the lungs. With each in-coming breath, cool air (and oxygen) is exchanged
for warm, exhaled air. When the number of respirations is faster than his heart rate, it is referred to as an inversion.
With sprint efforts, both heart and respiratory rates should recover to at least
60/60 (beats per minute/respirations per minute) within 30 minutes following cessation of exercise. For moderate exertions, recovery should return to a heart rate (HR) less than 60 bpm (beats per minute) within 10 minutes. Dehydration notably slows heart rate recovery. Persistent elevation of heart rate indicates that the horse is not coping well with the demands of the effort and
may be in metabolic distress. Poor recovery may signal an impending metabolic collapse due to the combined effects of dehydration, energy depletion, electrolyte losses, and heat build-up in the muscles.
EXTENUATING FACTORS
Hot weather is not the only factor contributing to developing cardiac/respiratory inversions, dehydration, or signs of heat stress. A horse ridden at too fast a speed for his level of condition generates excess body heat. A horse sporting a full hair coat is at risk of over-heating since hair insulates against heat dissipation. This can be managed by clipping, paying particular attention to removing hair on the neck, chest, and underbelly. Heavily muscled horses, such as Quarter Horses, Warmblood breeds and many gaited breeds are at greater risk of retaining heat in the working muscles in comparison to leaner breed horses such as Arabians or Thoroughbreds.
An overweight horse with abundant fat layers beneath his skin cannot dissipate heat effectively. Not only does excess body weight interfere with normal cooling processes, but fat also reflects a lack of fitness. Adequate preparation and training develop a horse into a sleek physique, building muscle where once there was fat. Conditioning expands capillary
Heavily muscled horses, such as Quarter Horses, Warmblood breeds, and many gaited breeds are
at greater risk of retaining heat in the working muscles in comparison to leaner breed horses such as Arabians or Thoroughbreds.
beds and blood flow within skin and muscles to improve circulation of oxygen in the tissues and flushing of heat to the skin surface.
Transport of a horse in an enclosed van in hot weather also contributes to dehydration and heat stress. A horse that has shipped from a distance away and has not been acclimated specifically to exercise in hot and humid conditions is ill prepared to deal with the added stress of the environment, no matter how fit the athlete. Most horses need at least three weeks in a strikingly warm climate to enable their bodies to learn to dissipate heat more efficiently.
WHEN TO TAKE A BREAK: SIGNS OF FATIGUE OR HEAT STRESS
Your horse’s external signs of heat stress may range from subtle to obvious. If he exhibits
any of the following signs, stop, and cool down
VETERINARY VIEWS
SPEEDHORSE August 2023 93
When the number of respirations is faster than his heart rate, it is referred to as an inversion.
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