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Nutrition Feeding for Summer

As with all times of year, what you feed your horse in summer depends on factors such as their level of work, age and size. However, feeding horses over summer comes with some unique challenges, writes LEISA HOFSTETTER.

The increased ambient temperatures associated with the summer months can affect a whole range of factors associated with feeding your horse the right feed. But it’s not only the temperature that changes over summer. The nutrient content of grasses and other forages change during this time too!

Increased ambient temperatures in summer may affect what you should feed your horse. Aspects of your horse’s feed that might need to be modified include electrolytes, the type of energy source, and water intake.


Electrolytes lost when your horse sweats should be replaced by adding them to their feed.

Electrolyte levels in your horse’s feed may need to be different in summer because an increase in ambient temperature means your horse will sweat more than in the cooler months. Because electrolytes are lost in sweat, the more your horse sweats, the more electrolytes you will have to add to their feed. Be careful not to oversupply electrolytes though, as this can have the opposite effect to the one you are trying to achieve.

Fats vs carbs

When horses digest their food, a lot of the energy is lost as heat. This generated heat can be a potential problem in summer for horses performing moderate to high intensity work, such as race horses and show jumpers, as they can overheat. Theoretically, a diet with a reasonably high fat content will generate less heat in digestion than a diet with the same amount of energy supplied by carbohydrates. It may therefore be useful for horses in competitive work over summer to increase the fat content in their ration and lower their carbohydrates. The opposite may be true in winter. If your horse needs to generate heat to keep warm, their body will consume energy to do so. It may be more efficient to feed more carbohydrates and less fat in the cooler months because heat generation is more efficiently sourced from carbohydrates than fats. However, roughage in forages such as fresh grass and hay should still make up the majority of a horse’s diet, no matter what the time of year.

But what about protein?

Protein, such as that found in oats, is another energy source that could present a problem if fed in excess during the heat of summer.

Protein is quite an inefficient source of energy. Proteins are made up of chemical building blocks called amino acids, which are vital for a lot of different body functions in both horses and humans, so it shouldn’t be disregarded in a horse’s diet. But if you are aiming to get the most out of energy supply, protein is not the way to go.

When protein is converted to usable energy in the horse’s body, a lot of heat is produced for a small amount of energy in comparison to carbohydrates or fats. So protein is another energy source that could present a problem if fed in excess in the hotter ambient temperatures of summer, especially for horses in heavy work over long periods of time, like endurance horses. Horses overheating can be just as detrimental as it can be for humans, and can even be fatal if not treated quickly. But the most likely side effect of too much protein can be excess sweating, which as you read earlier, comes with its own host of problems due to electrolyte loss.


Forages such as grass and hay should make up the majority of your horse’s diet, at all times of the year.

Forages such as grass and hay should make up the majority of your horse’s diet, at all times of the year. There are actually some variations in types of grasses that may affect what you feed your horse in the remainder of their diet. There are two main types

of grasses, cool season and warm season. The differences in cool versus warm season grasses can be quite distinctive. Some obvious differences include the types of sugars present in the grasses and the presence or absence of calcium compounds called oxalates. In sub-tropical climates such as the Far North Coast of NSW, warm season grasses are prevalent.

Warm season grasses are those species of grasses that grow to maturity and produce seeds in the warm seasons of the year. The opposite is true of cool season grasses. Often warm season grasses are high in oxalates. Oxalates are compounds that bind calcium in the digestive system of the horse and prevent it from being absorbed into the body. This can cause a deficiency so severe that calcium will be taken from the bones to compensate for the lack of calcium available for important bodily functions. A calcium deficiency can sometimes be visually obvious, such as with the symptoms of big head disease.

Warm season grasses

The nutrient content of grasses change during summer.

But what does this have to do with summer? New growth of warm season grasses containing oxalates tend to have a higher oxalate content than the same grasses in later stages of maturity. So this means that in spring, during the beginning of the growth stages, the oxalate content in warm season grasses will be higher than in summer, when the grasses are more mature. But because of these growth stages, there may even be variations in oxalate content in warm season grasses within the summer months, with more oxalates being present in early summer than later in the season.

There is another factor to consider when looking at the maturity stage of grasses. You might have observed that your horse prefers new growth grass to tall, well developed grass that is ready to produce seeds. For horses, the palatability of new grass certainly seems much greater than for mature grasses. In addition to palatability, digestibility also decreases as grasses become more mature. This is because mature grasses contain more structural carbohydrates such as cellulose, hemicellulose and lignin than new grass.


Lignin is a nitrogen containing compound that helps to give grass stems their rigid structure. Cellulose and hemicellulose also play a role in the structural component of grasses, but where cellulose and hemicellulose are digestible in the horse, lignin is not. Humans cannot digest any of these structural carbohydrates, which are often referred to as fibre. It is only because of certain microflora in the hindgut of a horse’s digestive tract that they get any nutrients from cellulose and hemicellulose at all. These microbes are able to do the digesting for the horse.

As digestibility decreases in more mature grasses, so does the energy the horse is able to absorb from the grass. This means warm season grasses in spring and early summer will give the horse more energy than those same grasses in late summer. This also has implications for horses at risk of laminitis, in that there are more starches and sugars in early stage growth of warm season grasses than mature warm season grasses. Starches and sugars affect insulin levels, which can affect laminitic horses or those at risk of laminitis.

Factors to consider

Feeding horses in summer comes with a range of unique challenges. Ambient temperature and seasonal growth of pastures can affect what you should feed your horse, and it’s important to consider all the factors affecting each individual horse. Your Equine Nutritionist can help to ensure that you’re feeding your horse correctly, no matter the season.

Leisa Hofstetter, BEqSc, is an Equine Nutritionist and founder of Hof Equine. Call her on 0415 120 454, email hofequine@gmail.com, or visit www.facebook.com/HofEquine