PG . 31
WHEN WATER ISN ’ T ENOUGH
ARTICLE BY : DR JENNIFER STEWART BVSC BSC PHD EQUINE VETERINARIAN AND CONSULTANT NUTRITIONIST CEO JENQUINE
SUMMER RIDING AND COMPETITIONS ARE AMONGST THE TOP FAVOURITE THINGS IN LIFE . THE CHANCE TO SPEND A SUNNY DAY OUTSIDE AND IN THE SADDLE IS HARD TO PASS UP - AND FEW ACTIVITIES RIVAL THE PLEASURE AND THRILL OF EQUINE COMPETITIONS . AN UNDERSTANDING OF HEAT BUILD-UP AND HEAT DISSIPATION ( COOLING ) ALLOWS US TO HELP OUR HORSES ENJOY SUMMERTIME AS MUCH AS WE DO . IT ’ S ALL ABOUT HEAT AND HUMIDITY .
Exercising your horse in summer when the weather is hot is different to exercising when it is hot AND humid or warm AND humid and even cool AND humid . This is because the horse ’ s cooling mechanisms are different when humidity is high .
At high exercise intensities , muscle heat production increases 40 – 60 times . When the temperature is 20 to 25 ° C and the humidity is less than 30 %, the heat generated by muscles during exercise can be easily cooled by the horse . To cool itself , blood is shunted to the skin and excess body heat is lost to the air . This is because when the air temperature is lower than the horses body temperature , the difference ( or gradient ) allows heat to freely moves from the horses ’ body into the air , allowing the horse to keep cool . But when the air temperature reaches around 32 ° C , the gradient is smaller . When body temperature = air temperature , there is no gradient to allow heat to move from the body to the air and blood shunting no longer results in cooling . Now sweating becomes the primary means by which the horse cools . Sweating wets the skin so cooling due to evaporation can occur . Sweating is the only way a horse can cool itself when air temperature is close to body temperature . However , when humidity is high , the water gradient between the skin and the air decreases , limiting the ability of the body to lose heat by sweating . This poses a serious threat to the horses ’ ability to cool .
Heat stress can occur in all horses - and in a relatively short time if horses are unfit , the weather is hot and / or humid , or if fluid and electrolyte losses in sweat are not replaced . For horses performing period of intense exercise body heat production can raise body temperature by 1 ° C per minute and unless this heat is cooled , body temperature could continue to rise to 42 ° C which is close to the limits of life . When the exercise includes short bursts of strenuous , maximum intensity , overheating is a real risk . In endurance-type exercise , heat exhaustion is more often due to dehydration . Horses that have travelled long distances in the heat and sweated profusely , or have had water withheld because
AQHA JANUARY / FEBRUARY ISSUE 2022