Sweat breakout, sunstroke, heat stroke: Horses are much more sensitive to heat and high outside temperatures than humans. When a horse suffers from a heat stroke, the temperature regulation of its entire organism is disturbed, and a general rise of its core temperature occurs. If the head is exposed to the heat of direct sun radiation the horse can be attained by a sunstroke leading to central nervous disorders. Since both cases are associated with great suffering for the horse and may possibly end in death, horses should be properly protected from the influence of high temperatures during the summer months.

Horses have a greater active muscle proportion than humans. When the muscles are activated by exercise and training, they generate heat and the horse starts to sweat. During intense training a horse produces an average of 20 liters of sweat. In humid heat, the produced amount of sweat does not increase significantly. Only approximately 10 more liters are produced, which does not significantly increase cooling. In addition, the hot air reaching 30 degrees or more during the warm summer barely provides cooling. On hot days, when the horse stands in a warm breeze, the so-called evaporative cooling remains with virtually no effect. In this case, the sweat runs down the horse’s body  and the important cooling mechanism is not functioning. In addition, as the sweat of horses contains high concentrations of minerals and trace elements, the body loses high amounts of important electrolytes. Extreme sweating therefore leads to a progressive demineralization of the metabolism. The loss of electrolytes causes disruption of the cell metabolism, for which vital minerals are urgently needed. Symptoms of electrolyte loss include muscle spasms, arrhythmia and nerve damage. Therefore, in case of heavy sweating, a horses feed or water must be supplemented with an electrolyte substitute.

Systemic overheating
Horses overheat up to ten times faster than humans. If the horse is continuously exposed to high outside temperatures, high air humidity and even training, its body continuously generates heat which cannot properly be regulated by its organism. This causes heat accumulation and heat stroke. Especially on hot and humid summer days, the danger is great. In temperatures of 25 to 30 degrees already moderate exercise during a quarter of an hour is already sufficient to raise the horses body temperature to a dangerous level. In us bipeds it takes up three to ten times as long to reach such an increase. The temperature sensation of the rider must therefore by no means be decisive, whether the weather is still appropriate for riding and training the horse or not. The heat accumulation stimulates the metabolism, leading to even more heat production until the blood circulation gets affected and the tissues are depleted of oxygen. This leads to a gradual hyperacidity of the metabolism and to a rise in body temperature.

Symptoms of a heat stroke
The body temperature starts to rise up to 41 degrees. In the muscles even temperatures of 43 degrees can be achieved. At such temperatures, the proteins of the horse's body begin to destroy themselves. The horse begins to stumble and stagger, can be apathetic as in anesthesia, collapse or present with muscle cramps. The breathing is superficial and fast, while the mucous membranes gradually turn bluish.

Characteristic of a heat stroke is that the horse does not longer sweat and that the skin is completely dry and hot. In the further course it comes to a drop of blood pressure, colic and kidney failure. In particularly dramatic cases, overheating of the horse can be fatal. This is a great danger especially for old or weak horses in bad condition and must always be kept in mind. Overheating of the horse is therefore always an acute emergency and a veterinarian must be called immediately.

The development of a heat stroke requires high humidity and compromised evaporation. Badly ventilated stables with a low ceiling, narrow vans, tournament tents exposed to the sun, overcrowded barns, trains or planes with inadequate air conditioning are predisposing factors.

First aid in case of heat stroke
The first action to take is to bring the overheated horse in the shade. Here it should be carefully showered with not too cold water, always beginning with the legs, in order to avoid a shock. The blood vessels on the limbs are very thin and not enough cooling can be transported through them further into the body, so a sole cooling of the legs does not help. The neck and trunk must therefore be cooled directly with water. To achieve an optimal temperature drop it is important to hose the horse down for at least ten minutes. As the body responds to the short cold stimulus with a backlash and produces heat to compensate, shorter showers have exactly the opposite effect. Of course, this should be avoided under any circumstances. To achieve a long-term cooling effect, the horse's legs must first be pre-cooled for ten minutes to 15 degrees. To avoid tendon irritation the water jet should not be set too hard. Caution is especially advised in inexperienced horses. Manipulation of the water hose often scares young horses. They need to be trained slowly to be hosed off in order to avoid triggering a panic reaction.

More and more popular, but not really effective, are spray tips for the hose, that enrich the water with essential oils. These substances don’t reduce the cooling time and only slightly lower the leg temperature more than pure tap water. Also, they do not extend the cooling effect. The same can be stated about cooling gels. The contained ethereal substances refresh the legs, but do not attain the deep cooling effect of water. However, the only advantage of gels is their safe application. Since various substances in these gels might be on the antidoping list, it is better for competition riders not to use these products 24 hours before the show. Another practical cooling agent are brushing boots that previously be put in the freezer. They store the cold and slowly release it to the horse's legs.
A damp blanket also provides the horse with effective cooling. Until the veterinarian arrives, Carbo vegetabilis a homeopathic cardiovascular agent can be administered to the horse. As the swallowing reflex is disturbed by the restrictions of the central nervous system under no circumstances water should be offered to the horse. This can lead to aspiration of water, which in the worst-case can cause pneumonia. For the same reason, the horse should also be deprived of food.

Preventive measures

As always, the prevention of such a case is better than having to deal with the therapy of a heat stroke or a sunstroke. In summery weather conditions the prophylaxis begins with the horse’s husbandry. For example, care must be taken to provide adequate shade on pastures or paddocks ensuring that our four-legged friends hide from the blazing sun. If this is not possible, during the day the cool barn is the better place for the horse. While avoiding draught, in the barn sufficient air circulation and fresh air must be provided. Training or trail rides should take place in the early morning or during the late evening hours and riding in the blazing sun should generally be avoided. Especially when the outside temperatures rise so high that even humans do not want to move anymore.

Related to this context and with regard to animal welfare, it has repeatedly and widely been discussed whether it is still horse-friendly to compete at shows during the hot summer months. Facts as the ride on the sticky trailer, the excitement and tension on the showground and the waiting time in the stuffy van, certainly can entitle to doubt.

When the sun rises above the head - the sunstroke
The sunstroke is caused by the direct influence of sun radiation on the horses head and needs to be distinguished from heat accumulation. A result is an increased blood flow to the brain and meninges, causing a swelling of these areas. This leads to central nervous disorders, comparable to those of meningitis. Affected are horses on competitions, racetracks or in the field, whose heads are unprotected and exposed over a longer time period to the sun. Even pasture horses, which do not have sufficient shade, are prone for a sunstroke. If a horse lays in the blazing sun in the summer, it should better be checked whether it only holds a nap or may have collapsed. Classic symptoms of a heat stroke are a tumbling, heavy sweating, beginning apathy and disorientation.

In contrast to the heat stroke, the body temperature is not increased, so that the two incidents can be clearly distinguished from each other. The quickest way to help the sun struck horse is to bring it in a cool, shady place and to cool the head with water or an ice pack. A conservative bloodletting of 7-8 liters of blood can also be relieving. As this method is not without risk, it requires an experienced veterinarian to be on site. Depending on the constitution and stamina of the horse, consideration must be given to whether a bloodletting can be carried out or if a possible circulatory collapse may occur.