Dietary Fat – Friend or Foe?

If you were to conduct a survey at any equestrian event you would find that many riders are feeding some sort of dietary fat to their horse. If not corn oil or vegetable oil, then a commercial high fat feed or supplement. What advantage could feeding fat have for a hard working horse? Is oil the same as fat? Do we know for sure that a high fat diet is not detrimental to the horse? Feeding fat is relatively new and the research conducted so far has shown some conflicting results, so all of the answers are not yet available. In this article we are going to visit the topic of feeding fat to the performance horse, look at the advantages, and attempt to clarify some confusing facts.

What is fat?

The word fat brings to mind the thick, greasy drippings in the bottom of a frying pan. While this is indeed fat, there are many other forms of fat that may or may not be more appealing to the horse (and owner). The chemical structure of the fat dictates whether it is a liquid (oil) or solid (fat). For example, our previously mentioned bacon grease would be solid at room temperature and therefore considered a fat, not an oil. The structure of fats, also known as triglycerides, is basically shaped like an E (see Fig 1.). The backbone of the E is a molecule of glycerol which can be converted to glucose (sugar) when the arms are separated. The three arms are chains of carbon atoms called “fatty acids”, usually between 12 and 22 carbon atoms long.

Horse health - nutrition - fat

The shorter the fatty acid arm, the more likely it is to be an oil (liquid) at room temperature. So when we discuss adding fat to the diet, it is just a general term to denote either fat or oil.

The type and structure of dietary fat can affect many elements in the body, right down to individual cell membrane structure. Each body cell has a skin-like membrane surrounding it. The cell membrane is composed mainly of a type of fat known as phospholipid. Changes in membrane structure can affect the way in which molecules such as oxygen glucose and waste products pass in or out of the cell. The type of fat fed can eventually influence all body systems by altering the structure and functional characteristics of these membranes.

Intensive research is being conducted in an attempt to improve the understanding of how different fatty acids affect human health. How applicable this research is to the horse is not yet clear. Most of the concerns in humans concern the correlation of high fat diets with the increased incidence of cancer, heart disease and immune function diseases. These are not necessarily applicable to the horse. A high fat diet for a human is defined as over 30% of total calories from fat; whereas a high fat diet for a horse is usually less than 10% of total calories from fat.

Concerns regarding the relationship between fat and chronic heart disease may be unfounded in the horse because the comparative life span of horses is too short for this slow developing disease.

Despite lower levels of fat in the diet of horses compared to humans, the long term feeding of added dietary fat to the horse is not very well understood because the practice is a relatively recent phenomenon. Research studies are usually very short – most not more than four months – although Kentucky Equine Research (KER) has conducted studies on feeding different fats to horses for as long as 18 months. So far, none of the studies have found detrimental effects. As more and more horses are maintained on high fat diets for the majority of their lives, there will be more opportunity to develop a better understanding of the influence of high fat diets on the health and well-being of the horse.

How well can the horse utilize dietary fat

Fat might be used in a horse’s diet to improve performance (both for endurance and high intensity exercise), maintain weight, improve coat and skin condition or increase the energy density of the diet. Can added dietary fat improve performance even though it is not a common part of the diet on which the horse evolved? Actually, there is a small percentage of fat in the basic horse diet of grass (1 – 4%) and even in the modified diet of oats (4-5%) and hay (1-3%), so having fat in the diet of the horse is not completely contrary to the way his digestive tract has evolved. In fact, the horse digests fat better than its herbivore counterparts: cows and sheep. Horses can tolerate up to 20% of their diet as fat, although in practice, this much is rarely ever fed.

Ideally, fat is digested in the small intestine. The greatest advantage of digesting fat in the small intestine is that it can be absorbed as is. In the large intestine and caecum fat is processed by micro-organisms, and too much fat passing through to the hindgut can upset the delicate balance of microbes, causing digestive disorders and interfering with absorption of some nutrients. Signs of too much fat in the diet include diarrhea or loose, cowpat-like droppings which have a strange soapy cast to them. When introducing fat to a horses diet it needs to be done gradually to allow digestive processes to adapt to the high fat diet – e.g. with oil, add 50ml oil every 3 days so it takes 2 weeks to build up to a cup per day. With high fat feeds and supplements, build up intake slowly over 7 – 10 days.

Where do fats go once they are absorbed from the small intestine? They eventually make it into the bloodstream, and then pass through the liver. The liver directs fatty acids to where they are needed. If the body needs energy for muscle contraction (ie exercise), then fat is directed to the muscle where it is broken down and used for energy. If the body does not need the fat at the time, then it gets stored away in adipose tissue (body fat) which can be found throughout the body.

Horses take time to adapt their digestive and metabolic processes to a higher fat diet. It takes 14 – 30 days to adapt the digestive system and a minimum of 30 days to switch on the metabolic processes in the muscle to utilise fat as an energy source in preference to glucose. It takes 3 – 4 months for muscles to produce aerobic energy at optimum levels using fat so it becomes obvious that the benefits of a high fat diet will not be evident overnight.

Another source of fat utilised by the horse is volatile fatty acids (VFA). These are the product of fibre digestion, produced by the microbes in the caecum and large intestine. These fatty acids are fairly constantly being produced as fibre passes through the digestive system. VFA’s are in fact, the horse’s main energy supply. VFA’s are very short chain fatty acids (two to four carbons) and are handled a little differently by the body than added dietary fat. One of the VFA’s: propionic acid, is a unique fatty acid in that it can be converted to glucose in the liver. The other main VFA’s: acetic and butyric acid, can be used for energy or stored in the adipose tissue.

How is fat metabolised?

For the body to get energy from fat, it needs to have some carbohydrate already spinning in the energy cycle. Since carbohydrate intake is not a problem in the horse this is rarely a concern. However, added dietary fat should be fed with some sort of carbohydrate, be it pellets or grain. Fat should be used as an energy supplement and not as the basis of a horse’s diet.

Fat is a less versatile energy source than carbohydrate because it can only be oxidised aerobically to produce energy. Aerobic metabolism (low intensity endurance type exercise) requires oxygen and is a relatively slow energy producing process compared to anaerobic (sprint exercise) energy production. Anaerobic metabolism does not require oxygen and can produce energy very quickly but is a far less efficient process. That means that if the horse needs quick energy for sprints or short bursts of speed, it will not be burning fat, but rather glucose from glycogen stores in the liver and muscle or blood glucose. Glycogen stores in the body are limited. Fat stores are enormous (depending on the amount of adipose in the body) so for aerobic work, the supplies are virtually unlimited as long as the body has some stores of glycogen or glucose (fat needs carbohydrate in the system to be metabolised). Long distance slow work such as trail and endurance riding depends mostly on aerobic metabolism and is an ideal situation for feeding fat.

Fatty Acid Content?

Fat is needed in the horse’s diet for absorption of the fat soluble vitamins A, D, E and K and as a source of the essential fatty acid- linoleic acid. Fatty acid composition is widely varied. Oils vary depending on the type of fatty acids attached to the glycerol backbone and the presence of saturated, mono-unsaturated or polyunsaturated fatty acids. Animal fats, coconut and palm oil are high in saturated fats whereas canola and olive oil are high in mono-unsaturated fats (omega 9). Other seed based oils or fish oil are high in polyunsaturated omega 3 or 6 fatty acids. The dietary intake of omega fatty acids can influence the fatty acid composition of the cell membranes and cellular responses. It is thought that omega 3 fatty acids may suppress inflammatory responses and omega 6 fatty acids may increase inflammatory responses and there is data showing these benefits in man and dogs.

A recent study at the University of Kentucky showed benefits to exercising horses from omega 3 supplementation in the form of fish oil. The addition of fish oil changed lipid (fat) metabolism and may have affected insulin sensitivity and glucose metabolism in response to exercise. Treated horses had lower heart rates during an exercise test, which may reflect reduced effort to attain a particular speed.

The optimum omega 3 intake or omega 3:6 ratio for horses is unknown, but it may be worth considering omega 3 intake in horses that are intensively exercising or those with chronic inflammatory disorders such as Queensland itch and other allergic skin conditions, arthritis, allergic lung disorders and recurrent laminitis. They won’t cure the problem but may reduce the severity or allow a reduced dose of anti-inflammatory medications.

So if omega 3 fatty acids are useful how can you increase the intake by the horse? Grains are high in omega 6 whereas grasses and forages such as hay are high in omega 3. Different oils have different omega 3 content. Linseed and fish oils are highest but are less palatable and it is difficult to feed high levels as an energy supplement. Canola is a palatable oil with a good balance of omega 3 and 6 oils. Corn oil is very widely used but is low in omega 3 and high in omega 6. Oils high in omega 6 linoleic acid such as corn, sunflower and safflower oil will do the best job of coat conditioning. Remember that the main reason for feeding oils is for energy so don’t concentrate too much on the omega 3 issue as we don’t fully understand the implications in horses yet.

What are the advantages of feeding fat?

As previously mentioned, some major reasons for adding fat to the horse’s diet are to promote a gain in body condition, improve hair coat, increase the energy density of the diet, and improve performance. Performance related benefits include lower lactic acid accumulation, reduced severity of tying up and muscle damage and better behaviour with a diet that is still high in energy.

An increase in the amount of fat in the diet has been found to increase the amount of oil in the skin of the horse. This increase in oil in the skin means a shiny, sleek, healthier-looking coat in 4 to 5 weeks. Traditionally, linseed has been fed because it was found to give the horse a nice coat This was because of the high fat content of linseed (around 30%). However, linseed releases toxic cyanide when the seeds come into contact with water and must be boiled to prevent cyanide poisoning which could kill the horse. Similar beneficial effects have been seen with the addition of almost any source of fat. Improvements have also been noted in hoof quality from the addition of fat to the diet.

Fat is more energy dense than any other horse feed. The same weight of fat has about two and half times as much energy as corn and three times as much as oats. For example, one cup of corn oil will provide the same amount of energy as ¾ kg of oats or half a biscuit of good hay. Horses in heavy training have a very high daily energy requirement and these horses often cannot or will not eat enough feed to meet their energy needs. The result is a steady decrease in body condition and reduced performance. In these instances, adding fat increases the energy density of the diet so that less feed and less grain is required to maintain body weight. The same situation applies if a gain in condition is required in a spelling horse, show horse or sales yearling. Adding fat to the diet can speed up the ‘fattening’ process or importantly reduce the amount of grain you need to feed. High grain intakes can lead to digestive disturbances, colic, laminitis and a number of other undesirable side effects.

Dietary fat can improve performance in a variety of ways. It has been found to be glycogen sparing, produces relatively little heat, can reduce lactic acid build up after fast work, can be helpful in preventing or reducing the severity of tying-up, and even help to calm horses that become ‘fizzy’ with high grain diets.

When the body is burning fat, it produces less heat than when burning other sources of energy, such as starch or fibre. Contrary to the popular belief that fat is a “hot” feed, it is actually very useful in hot weather. It does not heat up the body internally as much during times when the horse is already having to deal with external heat that reduce it’s ability to cool itself. For example, horses at the 1996 Olympic Games were being fed as much as four cups of corn oil per day to help them perform in the midsummer Atlanta heat and humidity.

Replacing the major portion of starch in the horse’s diet with fat is becoming popular as a treatment for horses with muscular problems such as tying-up. The type of muscle problem where high fat diets have been the most successful are in horses with equine polysaccharide storage myopathy (EPSM). These horses have a problem with storing excessive amounts of muscle glycogen and respond well to decreasing the amount of starch in the diet and replacing the required energy with fat. Research at KER has shown that horses prone to tying up had lower muscle enzyme levels after work when fed a high fat rather than high grain (carbohydrate) feed.

Perhaps the most practical advantage of feeding fat to the horse is the calming effect that has been noticed as compared to equal energy levels of starch. Added dietary fat slows down stomach emptying, thus slowing passage of feed through the system thus modifying the glucose and insulin response to feeding grain. Trials at KER have shown that adding oil to a sweet feed dramatically reduced the glucose and insulin response to a grain meal. Rising and falling blood glucose and insulin seen after a grain meal (starch) can have dramatic effects on the mental attitude of some horses. When a portion of the grain is replaced with some type of fat, the fluctuations in glucose and insulin are much smaller, resulting in a less reactive horse. The same response may also benefit the young growing horse that has a risk of OCD development – a study has recently been completed to evaluate the link between glucose and insulin levels after feeding and later OCD development. Preliminary results seem to suggest a link between glucose index of a feed (and insulin response) and the subsequent incidence of OCD development.

Which is the best form of fat?

Numerous digestion studies have confirmed that fat is very palatable and well digested by the horse. Individual preference will dictate which is the best source; it does not matter what advantages one type has over another if the horse will not eat it! Studies on palatability have found that normally corn oil is the preferred taste. Other oils, such as soybean, canola and safflower are also very well tolerated by the horse. Palatability tends to decrease in the animal fats and a big difference is found in the digestibility. While oils have been found to be up to 95% digestible, animal fats are significantly lower, closer to 75% digestible. So, for the same amount of fat, the horse would get 20% less energy out of the animal fat than out of the oil. Digestion studies on stabilised rice bran (KER EQUI-JEWEL) have found that fat from rice oil is also very digestible and highly palatable.

Fat can be found in other sources such as rice bran (20% fat), sunflower seed (25 – 40%), full fat soy (20%), copra meal (8%), high fat feeds (6 -12%) and raw linseed (30%). Since each of these products is lower in fat than oil (which is nearly 100% fat), more of the product will need to be fed to achieve similar fat intakes. An advantage of these other fat supplements is that they offer other nutrients besides fat and energy, they are often more palatable to horses and they are easier to feed. EQUI-JEWEL has added calcium, vitamin E and selenium. Rice bran has been a popular energy supplement in the USA for some years. It is presented in a palatable extruded micro-pellet that is easy to feed and is eaten more readily than oil when mixed in a feed. Half a kg of EQUI-JEWEL supplies the same calorie intake as a cup of oil. Research has shown that horses fed EQUI-JEWEL had lower heart rates and lactic acid levels during strenuous exercise than when they were fed corn oil. This means horses fed EQUI-JEWEL will have greater stamina and endurance than if they were fed corn oil. Whatever form of fat is chosen, it is essential to avoid feeding rancid fat. Horses tend to be very sensitive to rancid fat and will very quickly refuse to eat if they can smell the slightest hint of a problem. If horses eat rancid fat, it contains free fatty acids and peroxides that can cause problems such as reduced digestion and interference with utilisation of vitamins A, D and E, and interference with liver function. When purchasing fat, whether it is a commercial high fat feed or a bottle of oil, care should be taken to prevent the fat from going rancid (oxidising). It is best not to buy more than can be used in a short while. Particularly with hot conditions and commercial feed mixes, buy only what can be used in a month. EQUI JEWEL is stabilised to prevent rancidity, and has a shelf life of up to eighteen months. Keep anything with fat stored in a cool, dry area. Oils should be stored in the dark and added right before feeding in order to minimise oxidation from air contact.

Oils vary in their stability depending upon the chemical make-up and type of processing or handling. Cold pressing produces a stable oil such as canola oil which is quite stable whereas polyunsaturated oils such as fish oil are less stable and are prone to going rancid. Some cheaper oils are recycled and the initial heating process increases the degree of oxidation and presence of anti-nutritional factors. Whilst these oils are cheap, they can also be nasty and should be avoided in performance horses.

How much fat should I feed?

Some people think they are feeding a high fat diet when they add a teaspoon of oil per feed but this amount will have no impact on the fat intake of the horse. If you feed a commercial feed the feed will be labelled with the fat content. The higher fat content feeds have higher digestible energy (DE) levels. High fat feeds are those with above 6% fat, however when the fat content goes above 8%, palatability maybe reduced unless the feed is diluted and well mixed with chaff or other grains.

If fat is added as oil you need to feed half a cup per day to get the coat benefit and at least a cup to get a significant boost to energy supplies and utilisation. The amount of oil needed will be reduced if other high fat feeds are fed such as sunflower seeds or rice bran. Up to 4 cups of oil can be fed per day but this is best divided into 4 feeds and must be introduced slowly.


Feeding added dietary fat to a performance horse can help with the competitive edge. It should make a difference in the ability of a horse to maintain weight and give extra energy to reach the end of the trail. Finding the right source and the right amount of fat may be a matter of trial and error for each individual horse, but the rewards can make it well worth the effort.

By Kathleen Crandell, Ph.D & Peter Huntington BVSc
Kentucky Equine Research
Brighton, Victoria, Australia