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Feeding Your Horses in Summer

December 2017 by Tania Cubitt, PhD,

In Australia and the tropics of Asia, horses endure severe extremes in temperature and humidity. This can dramatically affect their health and performance if not managed correctly.

High temperature, high humidity, lack of air movement, poor ventilation, dehydration and exposure to direct sunlight all increase the danger of serious heat and heat-related problems for humans and horses alike. Horses are no exception, especially when they are expected to perform at intense levels.


Anhidrosis, which comes from the Greek meaning “without sweating”, is a condition primarily of horses in - and failing to adapt to - hot, humid climates. 

Although imported horses are reportedly most frequently affected, it can also occur in locally bred animals, and there appears to be no age, sex or significant breed predisposition. While there is an inherited component to this disease in cattle, this has not yet been established in the horse.

With constant humidity and high ambient temperatures, persistently elevated blood adrenaline levels may result, leading to ‘conditioning’ or insensitivity of the sweat glands to the affects of adrenaline. In turn, a progressive atrophy of these secretory glands may occur. 

Thus, initially horses may be seen to sweat copiously after exercise, but this gradually decreases over time until sweat patches are found only under the mane and tail. Although blockage of the sweat glands occurs in horses with anhidrosis, this is regarded as a secondary effect. The skin of affected animals is often scurfy, inelastic and there is frequently alopecia (hair loss) - most markedly around the face.

Horses that are dry-coated lose the ability to effectively dissipate heat through the evaporation of sweat on the skin’s surface and their core body temperature can rise dramatically, especially during exercise. In an attempt to reduce internal body heat, respiratory system stimulation occurs and this, in turn, leads to dyspnoea (difficulty breathing) and, if pronounced, acute respiratory alkalosis and possibly death. These animals are very susceptible to heat stroke and exercise intolerance may be so severe the animal is incapable of any form of work.

Recent research suggests the addition of certain amino acids and minerals in conjunction can aid and reduce the incidence of bouts of anhidrosis.

Does nutrition contribute to managing heat stress?

Electrolytes: A racehorse can lose up to 10 litres of sweat per performance (work/race). This fluid isn’t just water, it contains a lot of salts. These salts, when broken down into their chemical components, are referred to as electrolytes. These are typically groups of different salts that contain the essential electrolytes; - namely, sodium, potassium, chloride, magnesium and calcium. 

Electrolytes govern the transfer of water through cell membranes into or out of the cells. Thus, they function in getting the nutrients in and the waste products out. They are responsible for getting nerves to fire and muscles to contract. 

Essentially, all of the physiological actions in the body require electrolytes. And, importantly, they need to be present in the fluids in the appropriate amounts for these biochemical reactions to proceed in an orderly manner.

If we don’t provide at least a minimum electrolyte replacement, horses show up with such medical conditions as metabolic alkalosis, inefficient transport of oxygen and energy substrates, poor tissue perfusion, thumps, muscle spasms, exertional rhabdomyolysis, cardiac arrhythmias, gastrointestinal stasis, anhidrosis, kidney impairment and poor recoveries. In fact, poor heart and respiratory recovery is one of the key signs that can lead you to recognise the problems associated with the task of accomplishing thermoregulation. The point is most of these problems stem from dehydration and the resulting electrolyte imbalance.

The real question becomes, how much better could the horse do if they were in a state of ideal electrolyte and fluid balance? How many of the horses that fade in the last third or have prolonged recoveries after the event, could be winners if their electrolytes and fluids were balanced, and at appropriate levels?

Thus, it is essential to correctly manage and supplement horse diets with electrolytes. In the commercial world of equine nutrition, there is a plethora of electrolytes available. It is wise to carefully examine the labels of these products as many contain vast amounts of fillers and incorrect rations of electrolytes. Research conducted on horse sweat and sweat loss has resulted in products, such as HYGAIN® REGAIN®, being formulated.

Low heat feeding

Many equestrians already know about cool feeds, but what we are referring to is feeds that do not provide much heat, as a result of fermentation in the hindgut. This is done by processing grains, such as micronising them. 

Micronising enables nearly all of the starch in the grain to be digested in the small intestine, which results in little or no heat produced. Thus, the hindgut only has to digest the fibre in the horse’s diet which, in turn, dramatically reduces the amount of heat generated by fermentation in the hindgut.

Fat is digested quite efficiently in the horse’s small intestine and does not produce any heat whilst being digested. The problem, however, is high fat feeds in the tropics can quickly go rancid and mouldy. Antioxidants and mould inhibitors can be added to these feeds which, provided they are stored correctly, will greatly prolong the effective use by date of the feed.

Elevated environmental conditions reduce the horse’s appetite. Micronising improves feed efficiency, thus less feed is required to be fed to the horse. Also the micronising process enhances the palatability of grains and is a useful tool to help keep horses eating during times of environmental stress.

At HYGAIN®, our extensive range of horse feeds are designed to reduce thermoregulatory stress in horses using micronised grains and high fat feeds. Our feeds also contain elevated levels of electrolytes to ensure horses receive optimal levels of electrolytes.