Fats are a concentrated source of energy and are important for a healthy diet. They also supply fatty acids that have specific functions for health. Fats are important in the make up of vitamins A, D, E & K, the vitamins classified as fat soluble, and are a structural component of fat-containing hormones. Classifying fats may appear somewhat complicated in that their properties such as number of carbons, number of double bonds, placement of double bonds, and other structural components will influence their nutritional role. Like proteins and carbohydrates, fats are organic, made of carbon, hydrogen and oxygen, but contain a lot more carbon. More carbon translates to more energy being produced. Body fat functions to protect major organs, provide insulation, support regulating body temperature, and serve as an energy reserve when the diet does not provide adequate calories.

Although the horse’s dietary fat requirements are low, rations higher in fat will provide a good fuel source as a partial alternative to diets high in carbohydrates. Dietary fat is very digestible at up to 95% digested. Fats contain approximately 2 – 2 1/4 times more energy than an equal weight of most feeds classified as carbohydrate or protein sources. Therefore, adding fat to the diet will increase the energy density of the ration, decreasing the total amount of feed consumed daily.

Fat Requirements

Dietary fat assists in the absorption of the fat-soluble vitamins and supplies essential fatty acids. Horse requirements for the “essential” fatty acids (linoleic, linolenic & arachidonic) have not been clearly established or quantified. However, the essential fatty acids are generally important in promoting growth, supporting healthy skin and play a role in controlling inflammation. The designation of being essential is that they either are not made in the animal’s body or not made in adequate amounts. Equine nutritionists recognize there are essential fatty acids needed in the horse’s diet and that requirements will be relative to “what the horse does for a living.”

The higher fat content of balanced formulas does not mean that horses require higher levels of fat in their diet. Added dietary fat is a good nutritional management tool to fuel the horse, while also reducing feed amounts, and reducing the intake of dietary carbohydrates.

Fat Sources

Grass pastures contain low levels of fat. Horses are grazers and the types of fats consumed from grasses are classified as unsaturated. Vegetable oils (corn oil, soybean oil, canola oil, peanut oil and flaxseed oil) are the most common fats added to horse feed mixes or are used as a top-dress additive.

Most of the oils added to diets are easily consumed by horses and can improve palatability and preference. Rice bran contains approximately 15% crude fat and is fed as an ingredient in balanced formulas or top-dressed as a supplement. Although, horse owners must also be aware that rice bran alone has low calcium and a high level of phosphorus (see table below). Horse owners are encouraged to select a product that is stabilized and balanced for calcium and phosphorus.

Whole roasted soybeans have also been added to commercial feed mixes as a fat source in addition to providing a high level of protein. Animal fat is seldom used in horse diets, partly due to perception but also because plant sources are more palatable to the horse.

Summary of Selective Nutrient Content in Fat Sources

Numbers are based on as-fed or approximately 90% dry matter.

Nutritional Management Considerations with Fat Containing Diets

If adding an oil supplement as a top-dress start with ¼ cup per feeding and increase in ¼ cup increments. The maximum amount of oil that can be fed per day is relative to the amount of the concentrate being fed but should not exceed more than 15% crude fat of the total concentrate being fed daily.

Several studies have suggested that fat added to the diet can have a sparing effect (conserve) on glycogen. In other words, horses fed diets that are high in fat have higher blood glucose levels compared to horses fed low fat diets. Glycogen is a carbohydrate stored in the muscle that serves as a fuel reserve during exercise when there is inadequate oxygen supply for the cells. Horses that transition from aerobic exercise to anaerobic exercise may benefit from higher fat diets, including endurance, gymkhana, eventing, cutting/reining, and race horses.

Fat is very digestible compared to other fuel sources used by the horse. The high digestibility of fat translates to less body heat that is generated during metabolism thus a desirable energy source for horses working in hot and/or humid environments.

A horse’s gut is designed as a grazer, that is, a continuous eater. The horse’s stomach is small relative to total gut capacity and thus has limits with volume of feed consumed during a meal. Horses requiring high-energy intake will benefit from an energy-dense concentrate mix containing higher levels of fat.

Early lactation and intense to heavy working horses require energy rich diets. Added dietary fat allows energy to be added with less volume, more efficiently and safely to meet the increase in high-energy requirements.

Adding a fat source to a horse’s diet that is underweight is a solid nutritional management approach that minimizes issues associated with high grain feeds or excess volume of feed fed.

Other cautions that need to be considered when supplementing balanced rations with fats include the effects on the nutrient – calorie ratios.

Increasing the fat and reducing the starch content of a diet can lower the risk of colic and laminitis that is associated with high starch containing rations.

Final Thought

Mixing, or adding grains or any type of concentrate to a ration that is already balanced for the animal’s nutrient requirements is referred to as “cutting”. Cutting usually will imply that the nutrient-calorie ratios have been altered and that the balanced ration was most likely adversely affected. “Cutting” may also influence gut pH and gut microflora (bacteria that reside in the gut).

Obviously, the intention with adding feedstuffs is to improve the quality of the ration, but more often than not the animal’s diet is adversely affected with “cutting”. Cutting with grains or other feedstuffs will most likely adversely influence a balance formula and diet. However, the addition of fat within the limits already discussed does not appear to adversely influence the microflora of the gut or the pH of the gut. Usually there is an adequate safety margin with commercial balanced formulas so that adding 3 – 5% oil will not adversely influence the nutrient-calorie ratio.