Knowing how to adequately support your horse's health in hot weather is vital in order for normal functionality. As with most mammals, horses cool themselves by sweating, which has evaporative properties, helping to cool their core temperature.
A horse's thermal neutral zone is 40ºF to 77ºF, meaning that anything outside of this range puts additional stress on the horse's body. It is understood that horses need extra calories when temperatures fall below 40ºF, but it is not as well known what exactly the stress of 77ºF++ temperatures have on a horse.
Most horse's can acclimate to warmer weather in about 15 to 21 days. Once acclimated, the horse is more easily able to tolerate hot weather. Even when acclimated, make sure you're still looking out for your horse's health.
Some of ailments to look out for in hotter temperatures include:
Anhidrosis - the inability to sweat even when in heavy work
Dehydration - a deficiency of fluid within an animal
Test the horse's skin by pulling up a fold of skin at the point of the shoulder away from its body. Let go and count how long it takes to lay flat again. If the horse is dehydrated, it can take 6-10 seconds, versus the 1-2 seconds in a hydrated horse.
Some items to help: Apple Juice, Apple Elite Electrolyte
Bruised Hooves - the hard ground of summer can cause a horse to bruise their hooves, which can lead to secondary ailments including abscesses
Heat Exhaustion - a horse's internal temperature at 104ºF leads to poor metabolic system functioning - at just 105ºF, organ shutdown occurs and circulatory collapse can lead to death
If you notice your horse is profusely sweating along the shoulders, lower legs, neck, and hind-end, stop working immediately. To cool him faster, spray with cold water, scrape it off, and repeat until the water coming off of him is no longer hot.
Photosenitivity - this is commonly confused as sunburn, but is actually when a horse eats a plant where ultraviolet (UV) rays reacts with photodynamic compounds located inside the plant
Sunburn - Read this blog post for more information!
Conjunctivitis - This is also known as pink eye and typically occurs when a horse scratches their eye on their knee to get rid of insects. This can lead to rubbing bacteria the bugs carried further into the horse's eye. Excessive dust can also lead to conjunctivitis. This is not a contagious ailment in horses.
Sweet Itch - This is also known as Insect Hyper-Sensitivity and occurs from tiny midges biting a horse, typically on the belly, base of face/tail, or root of the mane. You will likely see your horse excessively itching or inflamed patches of skin.
Make sure that you know your horse's normal vital signs, so you can reference them when working in hot weather. The normal rectal temperature of a horse is 99.5-101.5ºF (can rise to 103ºF when in work). The pulse is 30-44 beats per minute. The normal respiration is 8 to 12 breaths per minute.
If you are concerned about your horse, make sure that you contact your veterinarian.