Heat and horses

Hot summers can be tough on humans, but they can be even tougher on horses. This is because, rather than choosing how to deal with the heat, horses rely on us to make the right management decisions.

The ideal ambient temperature for horses varies, but they are considered comfortable within a range of 0°C to 25°C. Horses tolerate cold better than heat. However, it is crucial to pay attention to extreme temperatures, both very cold and very hot, to ensure their well-being. Above 30°C, a heat alert should be activated.

Furthermore, the physiology of horses, while allowing them to be excellent runners, also makes them susceptible to generating a lot of heat during exercise. They generate a significant amount of metabolic heat during exercise because a large part of the energy used by their muscles is converted into heat (70%-80%).

Caballo al sol.

The sun also generates heat on the surface of a horse's skin. This heat buildup can cause various health problems if not properly controlled.

Horses are colloquially known as warm-blooded mammals, also known as endotherms, which are those that regulate their body temperature internally, regardless of the environment. This is achieved through metabolism, generating heat within the body. This is unlike ectotherms (such as reptiles), which depend on the environment to regulate their temperature.

Temperature regulation (also known as thermoregulation) is the horse's body's ability to maintain or restore its internal temperature.

With the constant fluctuation of ambient temperature, thermoregulation allows the horse to maintain its body temperature within certain limits. For horses to survive, their internal body temperature is maintained within a very narrow range, between 37.2°C and 38.5°C.

Termografía infrarroja de un caballo.

Heat is continuously generated in the horse's body as a result of metabolism and this increases during exercise.

Horses have a high metabolic capacity and, at the same time, a relatively small surface area for heat dissipation. Therefore, they are at a disadvantage compared to many other species. Horses must regulate their heat production and loss through thermoregulatory mechanisms.

To do this, they possess numerous peripheral thermoreceptors (sensory nerve endings) that detect temperature changes, generating corresponding nerve impulses. A coordinating center in the central nervous system (hypothalamus) receives these incoming nerve impulses and sends signals to the organs that alter body temperature, acting to reduce heat loss or eliminate accumulated heat.

Factors such as ambient temperature, high humidity, poor stall ventilation, prolonged exposure to direct sunlight, overwork, transportation (horse trailers and trucks can become very hot inside), and obesity can upset this heat loss/gain balance and cause horses to overheat.

A horse loses heat to the environment through a combination of radiation, convection and evaporation.

Radiation is the transfer of heat between objects without direct physical contact. Heat exchange by thermal radiation occurs between an animal's skin (or fur surface) and the surrounding environment through electromagnetic waves without direct physical contact. Solar radiation can be significant in hot environments, especially if the horse is exposed for long periods. A horse exposed to intense sunlight can absorb a large amount of solar radiation, which can exceed its metabolic heat production, potentially causing heat stress.

Convection is the upward movement of warmer areas and the downward movement of cooler areas. Convection occurs continuously between the body surface and the surrounding air. Free convection at the skin surface causes heat loss if the temperature is low, with additional forced convective heat transfer when wind blows over the body surface.

In the cold, a thick coat insulates and resists heat transfer by trapping air close to the skin, thus preventing heat loss. In summer, however, horses have a thin coat that facilitates heat loss.

Vapor por la evaporación del sudor.

If body heat is not minimized by convection, the horse's body temperature is regulated entirely by evaporation of sweat.

Horse thermoregulation depends primarily on evaporative heat loss through sweating. This evaporation occurs on the horse's skin surface and respiratory tract (panting). Horses sweat to maintain their core body temperature. And on hot summer days, horses can sweat, even if they don't move much. In cooler temperatures, sweat can evaporate quickly, creating a visible steamy effect.

The horse has highly efficient sweat glands, present in both hairy and hairless skin, producing the highest sweating rates in the animal kingdom.

Sudor y espuma por la latherina.

It has efficient evaporative cooling because its sweat contains a protein called latherin (the substance that causes sweat to foam), which acts as a humectant (surfactant); this allows sweat to move from the skin to the hair.

When horses generate more metabolic heat during exercise, the body activates heat-loss mechanisms to keep core temperature within the thermoneutral zone (the ambient temperature range in which an animal's normal metabolism can maintain a virtually constant body temperature without additional effort). The blood transports excess heat to the skin's surface, where sweat helps evaporate it.

Caballo sudado.

Sweat is a mixture of water, electrolytes, and proteins. Horses produce sweat as a thermoregulatory mechanism in response to homeostatic changes (adaptations the body makes to maintain internal stability in the face of fluctuations in the internal or external environment).

When horses sweat excessively, they run the risk of dehydration. A horse's body's water balance is controlled by hormone and electrolyte concentrations, so dehydration and electrolyte loss are closely related.

Electrolytes are minerals (calcium, potassium, sodium, magnesium, chloride, bicarbonate, and phosphate) that are involved in most of the electrochemical processes that sustain life. All are lost in prodigious quantities when a horse sweats. Fortunately, a horse can replenish its internal mineral reserves by grazing and drinking.

Caballo lamiendo sal.

Sodium is key to this; when blood sodium levels are high, antidiuretic hormone reduces water loss to conserve water and maintain this balance. Salt (sodium chloride) helps retain water in the body and encourages water intake, which is vital for preventing dehydration.

We must therefore supplement the horse's diet with salt to regulate the electrolytes they lose through sweat, especially in hot weather or when they are working. This helps prevent dehydration and promotes healthy muscle and cell function.

However, sometimes it may be advisable to administer a supplement; sodium isn't the only electrolyte lost in large quantities when your horse sweats. It also loses potassium, chloride, calcium, and magnesium, all important for the equine body's electrochemical processes. Therefore, any horse that works or sweats excessively in hot climates is a good candidate for electrolyte supplementation with a complete vitamin-mineral product. If lost electrolytes are not replaced, the resulting imbalance can lead to a drop in blood pressure, as well as neurological or cardiovascular problems.

Quality vitamin and mineral supplements are available in both granulated form, for mixing with feed, and in block form, for free-feeding.

Fosas nasales dilatadas de un caballo.

Another thermoregulatory system in horses is panting. Horses cannot pant like dogs, but they can increase their breathing rate to dissipate heat from their airways. As they exchange more air, this helps dissipate heat from the lungs and allows horses to release a significant portion of their retained body heat.

Panting is defined as a respiratory rate greater than 120 breaths per minute with the nostrils flaring and the horse adopting a rocking motion. Due to the high concentration of blood in the mucous membrane of the horse's upper respiratory tract, it has a very efficient and effective heat exchange system. It is estimated that this pathway dissipates almost 25% of the heat generated by the horse during exercise.

During exercise, blood vessels dilate, increasing blood flow to the mucosa and allowing more heat to be dissipated to the environment. When the airways maximize evaporative heat loss, the horse begins to pant. Respiratory evaporative heat loss allows for the cooling of venous blood draining from the face and scalp. This blood can be up to 3°C cooler than core body temperature, and upon entering the central circulatory system, it can have a significant cooling effect on the entire body. This system is likely an underappreciated and significant means of cooling the horse.

As we have seen, healthy adult horses can balance the accumulation and dissipation of body heat to maintain their body temperature between 37.5 and 38.5°C when they are in their thermoneutral zone (0°C–25°C). However, under certain circumstances, such as after intense exercise in hot or hot and humid conditions, body heat accumulation exceeds dissipation, and horses can suffer heat stress. Prolonged or severe heat stress can lead to anhidrosis (limited sweating), heat stroke, or brain damage.

Vigilaremos la temperatura en el van.

Many factors can determine a horse's ability to tolerate heat, including acclimatization, breed, age, feeding plan, physical condition, energy expenditure, hydration, and humidity. Horses transported in trailers over long distances may also be at greater risk due to poor access to drinking water and lack of airflow in the trailer.

To mitigate the negative effects of high heat stress on the body, early detection of heat stress and immediate human intervention are required to reduce the horse's elevated body temperature in a timely manner.

We need to know how to identify heat stress and heat exhaustion so we can help your horse quickly. Horses in hot climates or under heavy work should be monitored frequently for signs of overheating.

Symptoms of heat stress - overheating:

• High rectal temperature (39.5 – 41.5 °C)

• Increased resting heart rate

• Rapid breathing and flaring nostrils at rest

• Dehydration: loss of skin elasticity, sticky gums, sunken eyes, and reduced urine output.

• Exhaustion or lethargy

• Excessive sweating and hot skin.

• Reduced food intake

If we notice any of the clinical signs of heat stress described above, we will suspend all physical activity and take the horse to a cool place and cool it immediately.

Heat stroke symptoms:

• Very high rectal temperature (40.5 – 41.5 °C)

• Very fast heart rate at rest (more than 60 beats/min)

• Very rapid breathing at rest (more than 40 breaths/min)

• Stumbling, reluctance to move

• Lack of coordination

• Dehydration with prolonged reddened skin

• Agitation and distress

• Shock

• Collapse

Call your veterinarian and cool your horse immediately if it shows any of the above signs of heat stroke, immediate medical intervention may be necessary.

To detect dehydration there are two simple tests we can perform:

Prueba del pellizco.

1- The pinch test: We hold a fold of skin at the point of the shoulder and slightly pull it away from the body. We then release it, observing how long it takes for the fold to flatten. In a hydrated horse, the skin will return to its original position in less than a second. If the fold is still visible after two or three seconds, the horse is dehydrated.

2- Another test involves pressing your fingertip against the horse's gums. When you release the pressure, you'll see a white spot; observe how long it takes for the pink color to return. If the blood is hydrated normally, the pink color will return in less than two seconds. If the spot persists after three or four seconds, the horse could be dehydrated.

Overheated horses can usually be cooled with cool water from a hose or sponge. We spray the horse with a continuous stream, which helps dissipate heat, similar to sweating.

Refrescando a un caballo.

It was once believed that using cold water and ice on a hot horse to cool it down caused cramps. However, this myth has been debunked. Rapidly applying cold water and ice to the horse's body may cause mild cramps, but it is safe and can quickly relieve mild to moderate heat stress.

Cold water irrigation should be continued until the horse's core body temperature returns to normal. After hosing, the horse should be walked in a cool, shaded area. If there is no place to walk away from heat or direct sunlight, continue cooling the horse with water or ice.

Horses with heat stroke and rectal temperatures above 40.5°C may require additional measures to control symptoms.

We'll apply ice to the horse's forehead, head, neck, and back to cool the major blood vessels and the blood circulating throughout the body. As the blood circulates, this will help lower the horse's body temperature.

We'll avoid cooling the muscles in the back and around the rump. These muscles may have low blood flow, and cooling them can worsen the condition.

If the horse collapses due to severe heat exhaustion, we will continue to cool it from a safe distance until veterinary help arrives. Getting too close to a collapsed horse can be dangerous for both the handler and the horse if it tries to get up.

Horses should have access to clean, fresh water at all times, but it is essential to provide electrolytes in their drinking water to promote rehydration and electrolyte balance. Some heat-stressed horses may require intravenous (IV) fluids to replace lost water and electrolytes. Intravenous fluids are usually administered by the veterinarian through a catheter in the horse's jugular vein.

The best way to prevent heat stress in horses is to limit strenuous exercise in hot and humid conditions. However, for many competition horses, it is impossible to completely avoid training in hot climates.

Fortunately, there are several management practices that can be implemented to help horses regulate their body temperature and avoid dehydration and heat exhaustion:

• Give horses traveling to areas with different climates time to acclimatize to their new surroundings.

• Strenuous exercise and training should be avoided when the heat is very high, as much as possible.

• To reduce the risk of horses overheating, cooling equipment, such as fans, can be installed in stables and stalls.

• Access to clean, fresh water at all times.

• Some owners choose to clip their horses' coats in the summer, especially if they tend to have thick hair year-round. Clipped horses cool down better after intense exercise and may be at lower risk of heat stress.

• Cool the horse with hoses and fans after exercise.

• Always monitor your horse for signs of heat stress, such as rapid breathing and premature exhaustion.

Contact your veterinarian immediately if you suspect a horse is suffering from heat stress or heat stroke.

Despite all of the above, horses can live outdoors 24/7 during the warm summer months if, in addition to adequate forage, they are provided with two essential ingredients: fresh water and shade.

Caballos bebiendo agua.

Water , in particular, should be plentiful and readily available; horses drink more in the heat. Horses are sensitive animals and, like humans, have drinking preferences; they dislike drinking hot water in warm temperatures. Automatic waterers or large tanks, located in the shade and cleaned regularly, can be good options, though be sure to check the water levels periodically, as even automatic waterers can become clogged.

Horses typically consume around 5 liters of water per 50 kg of body weight, so a 500 kg horse will need a minimum of 50 liters of water per day. This amount can increase considerably during periods of exercise, in high heat or humidity, or in lactating mares.

Some horses may be more demanding with water than others. For example, older horses or those with dental or health problems may be more sensitive to temperature. We will carefully monitor their intake and drinking habits as each horse is unique. If the horse is hesitant to drink or shows minimal interest in water, the temperature may not be appropriate.

Let us never forget that they do not lack freely available salt.

As for shade, being able to escape the direct heat of the sun is essential. Shade can help prevent heat stroke or heat exhaustion in horses, just as it can in humans.

Caballos a la sombra bajo los arboles.

Shade from trees or shelters will protect horses from the sun. Trees are ideal, as one side will always be protected from the sun, while most shelters receive full sun part of the time. Keep in mind that shade changes throughout the day and shelters can block natural ventilation.

Horses often prefer to stay in the sun rather than in the shade, but they need the option; meadows and paddocks should always offer shade, even if they don't use it much. With rising temperatures, heat, and solar radiation, they seek shade and approach it even if they don't use it. Horses that don't have access to shade become stressed if they don't find it when they need it.

In short, horses are heat-sensitive and depend on humans to regulate their temperature, as they tolerate cold better than heat. They generate a lot of heat during exercise and have limited mechanisms to dissipate it, such as sweating and panting. Factors such as humidity, poor ventilation, or physical exertion can cause overheating, dehydration, or even heatstroke. It is essential to provide fresh water, shade, salt, and electrolytes, avoid exercise during hours of extreme heat, and monitor for signs of heat stress. If symptoms are severe, the horse should be cooled immediately and a veterinarian contacted.