The settled weather of summer means that for most horse owners it is their busiest time, with the daylight hours giving more time for riding and most equestrian disciplines having full event calendars. While New Zealand's summer temperatures are milder than in some parts of the world, they can reach significant heights in some areas and there are important feeding and management factors to consider to keep horses healthy and comfortable in the heat.

Water - The Overlooked Nutrient

Arguably the most important nutrient in the equine diet is one that often is not recognised as a nutrient at all. Water is the first limiting nutrient as horses cannot survive for as many days without it as they can without food. The amount of water required by the horse is determined by the magnitude of water losses from its body. These losses occur through faeces, urine, respiratory gases, sweat and, in the case of lactating mares, milk. Water intake varies depending on the horse’s physiological state as well as dietary factors, environmental temperature and physical exercise. While a 500kg horse at rest in a moderate climate will generally consume between 15 and 35 litres of water per day, this can increase when the temperature rises, and horses that are working and sweating regularly in warm climates can drink up to 100 litres per day.

Diet plays a major role in determining voluntary water intake and requirements. As a general rule, water intake is proportional to dry matter intake, but the composition and digestibility of the diet can alter this relationship significantly. Unless the water is unclean or unpalatable, horses will generally drink as much water as they require. Therefore, access to a clean and palatable water source at all times is essential to ensure optimum rehydration.

Fibre First

The way the equine digestive tract is designed means that horses are classified as monogastric hindgut fermenters. They have a small simple stomach and an enlarged hindgut, which comprises the caecum and colon, where billions of microbes dedicated to fibre digestion reside. The balance of these microbes is critical to digestion and overall health, and providing adequate fibre is one of the most important factors for maintaining hindgut balance and overall digestive health.

Fibre is best provided through pasture, hay and fibre products such as chaffs, beet pulps and soy hulls. For optimum digestion, at least 1.5% of the horse’s body weight in forage is required daily. This amount is mainly to ensure there is adequate buffering in the stomach and ensure the hindgut microbes have adequate fibre to ferment and stay in a healthy balance. Inadequate amounts of forage consumed daily can increase the risk of digestive problems including gastric ulcers in the foregut and hindgut acidosis in the hindgut.

Gastric ulcers occur through consistent exposure of the stomach lining to acid and are mainly caused by stress, inadequate forage and high grain meals. Symptoms include agitated behaviour, signs of discomfort while eating, and lack of weight gain. Because horses produce gastric acid in the stomach constantly, a consistent intake of forage is required to buffer the acid. Certain forages are more effective at buffering gastric acid, such as lucerne, and long-stemmed forages are preferred due to the longer chewing time creating more bicarbonate in saliva which also acts as a highly effective buffer. In the hindgut, acidosis can occur through inadequate forage causing the microbes to become unbalanced and the pH of the hindgut to drop. This condition causes symptoms such as loose manure, and mild colic and is implicated in the development of a debilitating hoof condition called laminitis.

As well as increasing the risk of digestive conditions, lack of fibre ingested often means that energy requirements are not being met which could result in weight loss. During the summer months when heat and lack of rain have caused pastures to dry off and grass to become scarce, alternative forage sources are often required to meet requirements. Supplementary forage through hay or baleage, chaff or fibre sources such as soy hulls and beet pulp are ideal in this situation. McMillan Grain Free is a blend of soy hulls and beet pulp which provides a fantastic alternative fibre source in this situation and is also formulated with added fat, vitamins and organic trace minerals.

Pass the Salt

Giving access to a salt block or loose salt in the paddock is a great way to ensure sodium and chloride requirements are met. Horses will actively seek out salt as sodium and chloride are the only two nutrients they have an appetite for, and free-choice salt will ensure requirements are met. Horses will often seek out salt and if available, most horses will consume sufficient amounts to meet their needs without overindulging. A balanced electrolyte that also contains potassium and magnesium will be required for working horses, especially during the warmer months.

Electrolytes are salts that play an important role in maintaining osmotic pressure, fluid balance, and normal nerve and muscle activity. The most important electrolytes are sodium (Na+), potassium (K+), chloride (CI-) and magnesium (Mg++). These are lost daily through sweat and urine in vast amounts when the weather is hot and the horse is working hard, trying to dissipate excess body heat. The major losses are of chloride followed by sodium and potassium. Therefore these are the most important electrolytes to replace.

All horses that work hard enough to break a good sweat will require electrolytes if they are to recover quickly and rehydrate. Travel and stress can also induce heavy sweating - a horse travelling a few hours to a competition on a hot day may lose up to 25 litres of sweat and if these losses are not replaced, the horse may start the competition already dehydrated. Some horses sweat more than others, so it’s important to monitor sweat loss to determine what needs to be replaced. Underestimation of sweat losses can occur on hot dry days due to rapid evaporation from the skin as the horse may dry quickly even though there has been a considerable electrolyte loss.

Substantial loss of electrolytes causes fatigue and muscle weakness, eventually decreasing the thirst response to dehydration. Research has also found that electrolyte deficiencies are a significant causative factor for muscle soreness and tying up in horses. The restoration of correct dietary electrolyte balance can significantly improve this condition. Since most of the electrolyte loss in the horse occurs through sweating, one method of calculating electrolyte requirements can be based on different amounts of sweat loss. Body weight loss during exercise is a good way to estimate the amount of fluid loss, where 1kg of body weight loss equals 1 litre of body water and salt loss.

Monitor Hoof Health

Hoof health is especially important in the dryer months, especially with horses working on harder ground. The nutrients needed for hoof growth — usually biotin, zinc, methionine and others — are often contained in a horse’s normal diet but adding a hoof supplement that contains these nutrients ensures that the horse has sufficient material to develop strong hoof tissue. Hooves grow slowly however and the outside of the hoof will not show the full effect of a hoof supplement for several months. For best results, use the supplement continuously in all seasons.

Take Cover

Providing shelter from the sun for at least some parts of the day through natural shelter belts or man-made shelters is very important, especially when horses are older or have pink skin that is at higher risk of sun damage. Some horses will require sunscreen or zinc on white or light-coloured muzzles to avoid painful burns.

Keep it Clean

Manure management is important to decrease flies and insects which can cause skin irritations during the summer months. The use of use fly sheets or fly sprays when required is also recommended as stamping at flies constantly uses a lot of energy and is hard on legs and hooves. To keep manure levels in paddocks low, collecting manure daily is the optimum method. When this isn’t convenient due to large numbers of horses, regular paddock changes are also effective. For parasite management, harrowing is only recommended when the weather is hot and dry as this ensures parasites are killed when they are spread. Cooler mornings and damp paddocks can mean the parasites stay alive and can result in them being spread throughout the paddock.

Consult with an Expert

While forage is the most important part of the equine diet, pasture, hay and fibre products will often not meet the requirements for many essential nutrients, especially if the horse is breeding, working or growing. Using a balanced NRM or McMillan feed at the correct level is a great way to complement forage and provide a balanced overall diet.
NRM and McMillan Feeds work closely with our technical partners Kentucky Equine Research, and have designed a wide range of equine feeds to suit all disciplines, all manufactured in New Zealand. From NRM Equine Balancer for ‘good doers’ that require nutrients without calories, to McMillan Rapid Gain for optimum weight gain and maintenance, all feeds have been formulated to provide New Zealand horses with the correct nutrition.

For assistance designing a balanced diet for your horse, contact NRM and McMillan Equine Nutritionist Luisa Wood.