Fats: Not Just an Equine Diet Fad

Fats serve many important functions for your horse, from increasing calorie consumption to reducing gastric ulcer severity

Society has seen its share of diet crazes, even in the past decade. From low-carb and high-protein to low-fat and high-fiber, trends have come and gone and come again, making food selection challenging. Luckily, horse owners don’t have as many options when they’re picking their charges’ feed. As herbivores, our horses’ diets must be high-fiber complemented by a commercial product fit to meet their life stage (performance, breeding, growing, etc.). The high-fat diet era began as a way to effectively increase calories without drastically increasing feed volume and, as researchers learn more about the benefit of fats for our four-legged friends, it appears that high-fat diets are here to stay.

What Exactly are Fats?

Fats and oils are part of a class of molecules called lipids. Structurally, all fats contain the following components:

  • A single glycerol molecule A chain of three carbon atoms, each with a hydroxyl group (oxygen and hydrogen) bound to it; and
  • Fatty acids Long hydrocarbon (containing, you guessed it: hydrogen and carbon) chains.

The fatty acids attached to glycerol vary in length and in how their own carbon molecules are linked. When single bonds link carbon atoms, the fatty acid is considered saturated. Saturated fat originates predominantly from animal fat sources such as tallow. Conversely, when one or more double bonds link the carbon atoms, the fat is unsaturated. Horse diets consist mainly of unsaturated fats such as vegetable oils.

Fats can be found in forages and grains in many forms, including di- and triglycerides, sterols, and phospholipids. The fats we typically supplement as oil are predominantly triglycerides. Each fat type varies significantly in its availability to the horse, which we will discuss later.

Digestion and Absorption

Once a horse ingests fat, enzymes (called lipases) in the stomach begin to break it down. A majority of fat digestion takes place in the small intestine, specifically in the duodenum and jejunum. After absorption, fats move along to the liver, adipose tissue, or elsewhere as needed for storage or use. Fats that do not get absorbed in the small intestine travel to the hindgut (the large intestine and colon), where they will be excreted in the feces.

In several studies researchers have found drastic differences in the digestibility of various fat sources in the horse’s diet. Fats from forages appear to be 55% digestible, whereas fats from oil are 100% digestible. This makes sense, considering that cell wall components more than likely surround the fats in forages and make them less available for digestion.  

Chew the Fat

Researchers have compared the palatability of both animal and plant-based fat sources to horses and found corn oil to be the most acceptable, but other sources can be just as readily consumed. See common sources of fat used in equine diets in the table below:

Source Avg. Fat (%) Points to Consider
Vegetable Oils
(corn, soybean)
  • Highly palatable source of calories
Soybeans 20.0%
  • Serves also as a quality source of amino acids
  • Contains trypsin inhibitors and must be heat-processed prior to feeding
Flaxseed 40.0%
  • High in omega-3 fatty acids
  • Due to hard outer coat, should be ground prior to feeding
Rice Bran 22.0%
  • Good source of fiber and contains gamma oryzanol, an antioxidant that might improve muscle quality
  • Inverted calcium to phosphorus ration
  • Contains a naturally occuring enzyme (lipase) that increases rancidity if not stabilized
Sunflower Seeds 45.0%
  • High in potassium and omega-6 fatty acids
Marine-Based Oils
(menhaden, herring)
  • High in omega-3 fatty acids
  • Odor can be a deterrent to horses and owners

Why Horses Need Them

“It is important to understand that there are two types of fats: dietary fats and polyunsaturated fatty acids,” says Stewart K. Morgan, DVM, PhD, clinical nutrition resident at the Virginia-­Maryland College of Veterinary Medicine, in Blacksburg. Dietary fats, also known as the triglycerides mentioned earlier, are a concentrated source of dietary energy that provides essential fatty acids (EFAs) and can carry the fat-soluble vitamins A, D, E, and K. Because hydrogen and carbon atoms make up these vitamins’ structure, they are hydrophobic in nature. Have you heard the saying “oil and water don’t mix”? Hydrophobic literally means “water-fearing” and describes oil’s propensity to separate from water. Therefore, fat-soluble vitamins need fats to help transport them across the small intestine. Extremely low-fat diets can potentially reduce fat-soluble vitamin absorption, as seen with decreased vitamin E levels in ponies fed an extremely low-fat diet.  

Meanwhile, polyunsaturated fatty acids can be metabolized to form compounds that serve biological functions. “These include omega-6 and omega-3 fatty acids, which are essential to the horse,” says Morgan.  

Horses cannot synthesize EFA on their own and rely on dietary sources to meet their needs. The two most biologically relevant EFAs, α-linolenic acid (omega-3) and linoleic acid (omega-6), play a vital role in the immune system, central nervous system, and cell membrane structure, to name a few. The average equine diet tends toward greater omega-3 intakes than omega-6.  

In a two-year study conducted at the University of Florida, researchers found that the fat content in bahiagrass (a warm-season pasture grass species) contains 40-55% omega-3 fatty acids and as hay contains 18-35%. Although hay and pasture are low in total fat content, typically offering less than 5%, most of the fat is made up of omega-3 fatty acids, whereas the fat in cereal grains, like what you’d find in horse feed, is made up primarily of omega-6 fatty acids.

Morgan says researchers are still trying to determine horses’ EFA requirements, but there is some evidence that horses might benefit from fatty acid supplementation in certain conditions. Currently, Nutrient Requirements for Horses (2007) suggests horses receive a minimum of 0.5% of dry matter in linoleic acid, equivalent to approximately 50 grams per day for the 1,100-pound horse. Nutritionists have yet to set an exact requirement for α-linolenic acid, but horses more than likely consume adequate levels with good-quality forage.  

What Do They Do?

Fats can benefit many aspects of a horse’s health. “Although a typical forage-based equine ration should meet a horse’s EFA requirements, there are benefits to supplementation under certain conditions, such as meeting a medical need to gain weight, managing inflammatory conditions like heaves and arthritis, or preventing and managing gastric ulcers,” Morgan adds. Owners of performance horses, especially those requiring a large amount of digestible energy to support high-intensity performance, feed fats to increase a meal’s caloric density without also increasing its volume. Let’s take a look at the unique benefits of fat unveiled by recent ­research:

Calories Pound for pound, fat contains 2¼ times more energy than do carbohydrates. Horses use fat for energy production without needing a drastic increase in feed volume. Broodmares and performance horses, as well as horses below ideal body condition, benefit from fat in their diets.

feeding fats to horses

Skin and coat condition Many owners supplement fats to add shine and brilliance to their horse’s coat. “Some supplement with flaxseed oil to improve a horse’s hair coat, but the efficacy and benefit to an animal fed a forage-based diet has yet to be determined,” says Morgan.

Performance and exercise Does adding fat actually improve a horse’s performance? It’s possible. Some of the theories behind fat’s role in improving performance include reducing feed intake, decreasing heat production during exercise, and sparing muscle glycogen, the storage form of glucose horses need to produce energy. Countless factors affecting performance, including training protocols and conditioning, confound the evidence and make it difficult to know for sure whether fat affects performance.

We do know that in low-intensity, long-duration exercise (think endurance riding), supplementing at least 8% fat appears to keep blood parameters such as glucose and free fatty acids closer to baseline. Researchers have also seen lower levels of plasma lactate in horses performing low-intensity exercise on this diet. These results suggest fat helps decrease carbohydrate use, having a “glucose-sparing effect.” The same cannot be said for high-­intensity exercise, such as racing, in which fat-supplemented horses did not use glycogen any differently than unsupplemented horses. This could mean carbohydrates play a larger role than fats in fueling higher-intensity exercise.   

Behavior When comparing calorie sources, some researchers have suggested that replacing typical grain diets or starch content with some fat can potentially reduce horses’ reactivity. Holland et al. observed less spontaneous activity (distance moved per day) and reactivity in horses fed a diet supplemented with 10% fat than horses fed a control diet with no added fat. In several studies fat-supplemented diets have resulted in decreased cortisol (the stress hormone) levels, even in young, growing horses. Foals fed a fat and fiber diet appeared less stressed and reactive after weaning versus those fed a traditional sweet feed. And in one study out of Spain, scientists found lower cortisol levels and startle reaction intensities when horses consumed high-fat diets versus a sugar and starch control diet.

Reproduction Adding fat to pregnant and lactating mares’ diets can be key to controlling meal volume when the high calorie requirements during early lactation mean feeding more concentrate per day. “For broodmares, the fatty acid profile of broodmare milk is influenced by the fatty acid profile of the diet, and for stallions there is evidence that diets supplemented with omega-3 fatty acids may improve fertility,” says Morgan. In fact, in studies, stallions supplemented with fish oil high in omega-3 fatty acids showed improved sperm production and motility over control stallions.  

Tying-Up Recurrent exertional rhabdomyolysis (RER) and polysaccharide storage myopathy (PSSM) are two equine muscle disorders. In Thoroughbreds with RER, substituting fat for starch in the diet actually reduced excitability and nervousness, known triggers for RER-prone horses, along with heart rate. Serum creatine kinase, an indicator of muscle breakdown, also decreased. Owners of horses with PSSM can lower the risk of tying-up episodes by feeding fat to reduce and replace glucose uptake and abnormal glycogen breakdown.

Gastric ulcers Substituting fat for nonstructural carbohydrates as a calorie source appears to help horses prone to gastric ulcers. Though there’s a lack of research in this area, we know that fat delays gastric emptying and reduces gastric acid production and could theoretically reduce gastric ulcer severity.

Insulin resistance Says Tanja Hess, MV, MSc, PhD, associate professor in equine sciences at Colorado State University, in Fort Collins, “Omega-3 fatty acid supplementation in horses may improve insulin sensitivity (the body’s responsiveness to insulin signaling the removal of glucose from the blood) in insulin-­resistant mares, as shown by a trend for improved insulin sensitivity in resistant mares supplemented with flaxseed or a marine supplement containing eicosapentaenoic acid and docosahexaenoic acid (forms of omega-3 fatty acids).”  

She also described a study (Brennan et al.) in which supplementation with docosahexaenoic acid decreased basal insulin and glucose in horses with dexamethasone-induced insulin resistance.  

Metabolism When mature horses consumed high-fat meals, as opposed to meals high in non-structural carbohydrates, researchers saw a decrease in both blood glycemic and insulinemic responses.  

It’s important to take caution when feeding a high-fat diet to ponies, however, especially when feeding above their caloric intakes. Researchers in Germany observed higher plasma glucose and insulin concentrations after an oral glucose test in Shetland ponies fed high-fat diets. Higher insulin levels combined with elevated glucose implies that a pony is insulin resistant. Also, avoid supplementing fat in diets for any horse or pony prone to hyperlipidemia (high levels of fat in the bloodstream), as this condition can be fatal.  

How long does it take to see these physiological changes associated with feeding fat or individual fatty acids? Nutritionists say a minimum of 10 to 12 weeks, although some researchers have reported changes in three to five weeks’ time. Consistent feeding is key to seeing results.

Take-Home Message

Dietary fats and essential fatty acids help meet a horse’s daily nutrient requirements but potentially provide other health benefits, as well. Morgan says that in any situation, horse owners should consult with an equine nutritionist to determine if and when they should add dietary fat or fatty acids to their horse’s diet.