b'eatH Learn how your horses internal thermostat works Handling the in extreme heat and ways to keep him coolCHRISTA LEST-LASSERRE, MAM aybe it was his name. The 18-handreduces heat, she says, through its interface with the air: one-ton Norman Cob named Texasskin. Thermal receptors in both the internal organs and the found himself in a very uncharac- skin send messages to the hypothalamusa small part of the brain responsible for many hormonal functionswhich then teristic heat wave last summer inactivates various thermoregulatory mechanisms to trap or northwestern France.release heat as necessary.While sweating is a good tool for dissipating internal heat, He can go 35 kilometers (22 miles) on an average day, andit is less effective in horses than in humanssimply because I usually drop him to 25 (15 miles) when its hot out, sayspound for pound and inch for inch, humans have much owner Fanny Chatel, who drove Texas in harness 1,550 milesmore skin surface area for their body size, says Dahlborn.across northern France last year. But 40C (104F)? ThatsFurther, due to their great muscle mass, horses produce just too much to ask. much more heat than we do and must dissipate the surplus Like many European countries, France experienced adespite the skin area disparity, says Cecilie M. Mejdell, DVM, major heat wave in 2019, bringing temperatures so high thatPhD, of the Norwegian Veterinary Institutes Department for the national equestrian federation had to adjust competitionHealth Surveillance, in Oslo. times to avoid putting horses at risk of heat stress. The horse can also use the respiratory system as a cool-Owners across the affected zones took measures to protecting mechanism. Horses cant pant like a dog, but they can their horses, providing shade and easing exercise routines.increase their respiratory rate to dissipate heat from the For Chatel, that meant a four-day hiatus from her four- airways, as they exchange more air, says Mejdell.month escapade in SaumurFrances equitation capital.The first line of approach for thermoregulation, though, is Im the one asking Texas to drive me on this exciting jour- the skins efficient and expansive vasodilation system, she ex-ney, Chatel says. Its up to me to make sure hes comfort- plains. When its cold, horses can close up the blood vessels able enough to do it. in their skin so the heat in the blood stays deeper inside the body. As temperatures increase, the diameter of those vessels A Primer on Thermoregulation also increases, routing as much as a third of the horses blood Like most mammals, horses come equipped withat a time to the skin alone, close to the surface and away complexand very effectiveways to thermoregulate, orfrom the internal organs, which get the chance to cool off. self-adjust their internal body temperature like a thermostat.This system, however, comes at a risk: When too much The primary goal of thermoregulation isnt comfort but, rath- blood gets pumped away from the internal organs, they er, survival, keeping the internal organs functioning properlycan suffer oxygen deficiencythe basis of heat stroke, says at the ideal equine body temperature of around 99.5 degreesBndicte Ferry, DVM, equine preventive health expert at the Fahrenheit, says Kristina Dahlborn, PhD, professor in theFrench Institute of the Horse and Equitation, in Saumur. Department of Anatomy, Physiology, and Biochemistry at the Swedish University of Agricultural Sciences, in Uppsala. All About SweatAmbient temperatures affect body temperature signifi- When horses sweat, it evaporates off their skin into the air, cantly. When its cold out, the equine body works to conservepulling with it body heat, resulting in a cooling effect. Horses and increase internal heat. On hot days it dissipates andhave a lot of sweat glands, and they can sweat profusely, 10August 2020The Horse|TheHorse.com'