Lori K. Warren, PhD, PAS
Department of Animal Sciences,
Institute of Food and Agricultural Sciences
University of Florida

Introduction
Adding fat to the horse’s diet has become increasingly popular in recent years. Whether it’s top-dressing corn oil, switching to a fat-added grain mix, or the convenience of “dry” fat in blended fat supplements, the diets of many horses are being affected by the fat-feeding craze.

Dr. Lori Warren

Dr. Lori Warren is an equine nutritionist and an Assistant Professor in the Equine Sciences program at the University of Florida. Her primary research interest includes studies with omega-3 fatty acids and Vitamin E supplementation and their effects on inflammation and immune system responses in horses. Dr. Warren received her M.S. and PhD in Equine Nutrition and Exercise Physiology from the University of Kentucky and her B.S. from the University of Wyoming. Prior to joining the faculty in Florida, she served as the Equine Extension Specialist in Colorado and the Provincial Horse Specialist in Alberta.

While the benefits of high fat diets for horses have been studied and realized, researchers and owners are now asking if one type of fat will offer greater health advantages over others. Human health has been shown to benefit from the addition omega-3 fatty acids to the diet. Can the same be true for horses? This article will address what omega-3 fatty acids are and what they may, or may not, do for your horses.

The Benefits of Going “High” Fat
Adding fat to the diet of horses is not a new practice. For years, horse owners have added a jigger of corn oil or a cup of boiled linseed to the grain ration to bring out the luster in the hair coat. However, it’s only been within the past 15 years that fat has been recognized as a valuable feed ingredient, and one with many advantages over traditional hay and grain rations.

Fat is a potent source of calories and is easily digested by the horse making it extremely useful in the diet of horses with high energy demands. Where we once relied solely on cereal grains to provide additional energy, we can now replace a portion of that grain with fat. In doing so, we may reduce the risk of digestive disorders associated with feeding large amounts of grain, which provide energy primarily in the form of starch. As a result, fat-added diets allow us a safer alternative to traditional grain mixes for putting weight on a thin horse or meeting the higher caloric needs of a high level performance horse or heavy milking broodmare. Furthermore, in situations where grain feeding is contraindicated, such as horses that have some forms of tying up or a past history of laminitis, fat can be used to help meet the caloric requirements when forage cannot do the job alone.

In addition to its use as an energy source, research has shown that fat-added diets may offer other benefits. Feeding a high fat diet to a performance horse may confer metabolic advantages that could delay the onset of fatigue and prevent them from overheating while working in the hotter summer months. Research, supported by numerous anecdotal claims from horse owners, has also reported that high fat diets make horses calmer and more level-headed compared to traditional grain mixes that have no fat added. Fat also provides the horse with a source of essential fatty acids and aids in the absorption of the fat-soluble vitamins A, D, E and K, which helps the horse meet these nutrient needs.

Obviously, we’ve come a long way from adding a small amount of fat to improve hair coat! Certainly a greater awareness of the merits of adding fat to the diet of our horses has made this practice increasingly popular. In fact, it’s getting harder and harder to walk into a feed store and find a grain mix that does not contain at least some level of added fat. Despite all of the positives we see when fat is added to a horse’s diet, some of us have started to wonder if there are also some negative consequences.

Not All Fats Are Created Equal
Fat is not a uniform material. Fat is composed of different fatty acids in the same way that protein is composed of different amino acids or a word is composed of different letters. Each fatty acid exhibits unique physical characteristics and each fatty acid has its own “job” or function. Some have greater potential to enhance, and others to harm, various biological processes in the body.

Even those of us who are not technically “health conscious” are aware that consumption of a high fat diet can adversely affect our health. However, saturated fats, which originate primarily from animal foods such as meat, milk or eggs, have been associated with greater risk for cardiovascular disease, compared to unsaturated fats, which are found in vegetable oils. This demonstrates that saturated and unsaturated fatty acids play differing roles in the body, beyond just serving as a source of calories.

The horse’s “high” fat diet will never approach the level known to cause health issues in humans. A high fat diet fed to a horse might contain 10% of the calories provided from fat, whereas problematic diets in humans are over 30% fat. In addition, the source of fat added to horse feeds has historically been from oils of vegetable origin, the most popular of which include corn oil, canola oil and soybean oil, which are high in unsaturated fat. Does this mean horses will not experience problems? Not necessarily, because not all unsaturated fats are beneficial.

Omega—Not Just a Letter in the Greek Alphabet
Similar to humans, horses require certain fatty acids in their diet. These essential fatty acids include linoleic acid, belonging to the omega-6 family, and linolenic acid, which is the parent of the omega-3 fatty acids (Figure 1). The horse does not have the ability to synthesize these fatty acids in the body, and therefore relies on what is supplied in the diet.

Both omega-3 and omega-6 fatty acids are unsaturated fatty acids; however, they have somewhat opposing roles. Once in the body, these essential fatty acids are transformed into potent, hormone-like chemicals that regulate many vital body processes, including blood clotting, inflammation and the immune system. In general, omega-6 fatty acids tend to stimulate blood clotting and inflammation, whereas omega-3 fatty acids tend to suppress these responses.

Blood clotting, inflammation and immune system responses are normal processes and are necessary for the body to fix damaged tissue and fight illness and infection. However, if these processes get carried away, they actually become harmful. Therefore, while omega-6 fatty acids, who promote these responses, need to be included in the diet, the ration must also contain enough omega-3 fatty acids to keep these processes in check.

Fat, it’s a good thing…right?
Despite the many benefits of adding fat to the horse’s diet, there may be reason to question what type of fat we should use.

One concern with fat supplementation is that we may be skewing the natural balance of omega-3 and omega-6 fatty acids the horse’s body is conditioned to receive. Hay and pasture forages are low in total fat content (~2%), but most of this fat is made up of omega-3 fatty acids (Table 1). Cereal grains, such as oats or corn, are also naturally low in fat (~3%), but provide primarily omega-6 fatty acids. Corn oil, soybean oil, canola oil, and rice bran are the most common fat sources added to horse feeds. Not only are these sources high in total fat content (25 – 99%), they also provide most of this fat in the form of omega-6 fatty acids (Table 1). Ultimately, a high-fat diet derived from these omega-6-rich sources may change the proportion omega-3 to omega-6 fatty acids, which could have adverse biological consequences.

Since domestication, our basic dietary management of horses has probably shifted the proportion of omega-3 and omega-6 fatty acids in the diet. Wild horses consuming all-forage diets followed the grass to new areas for grazing as the season changed. Their diets, although low in fat, contained much more omega-3 fatty acids than omega-6. Today, even horses that have been blessed with full-time pasture turnout probably do not fare as well as their equine ancestors. The grazing of today’s horses is limited to relatively smaller areas, which limits their selection, as well as their ability to roam to more productive stands of grass. In addition, most horses, even if pastured, will need to consume hay when grass goes dormant in the winter months. Hay, although still higher in omega-3 fatty acids than omega 6, contains less omega-3 than fresh growing grass. When we put the first horses to work, we started feeding grain, thus reducing the omega-3 content of their diet even further.

Because specific fatty acids can elicit different biological responses and influence critical chemical reactions, we may be inadvertently affecting the heath of our horses by what we are feeding them. Research is just now starting to address this concern, as well as determine if we can enhance certain responses or confer some sort of protection by supplementing the diet with omega-3 fatty acids.

What Do We Really Know About Feeding Omega-3 to Horses?
Throughout the past 10 years, omega-3 fatty acids have received a lot of attention in human nutrition. Our diets contain much more saturated fat and a higher proportion of omega-6 fatty acids compared to the diets of our prehistoric ancestors. Scientists are finding that dietary supplementation with omega-3 fatty acids may be useful in the prevention and/or treatment of heart disease, thrombosis, hypertension, renal disease, rheumatoid arthritis, inflammatory disorders, autoimmune disease, insulin resistance, and possibly cancer.

Because of the reported benefits of omega-3 fatty acid supplementation on human health, several equine researchers have become interested in determining whether horses will respond favorably to similar supplementation. Much of the investigation has focused on inflammatory and immune system responses. Although the number of studies in horses is comparatively limited, some studies have shown positive results of supplementing omega-3 fatty acids while others have found no effects. Unfortunately, determining recommendations for feeding omega-3 fatty acids has been made difficult because of the lack of consensus amongst the studies in the amount of omega-3 supplemented, the duration of supplementation, the varying “control” diets which served as the basis for comparison, and the source of the omega-3 fatty acids used.

The source of omega-3 fatty acids is likely very important. Omega-3 and omega-6 fatty acids are actually a “family” of fatty acids. While each fatty acid shares similar characteristics to others in its family, the biological activity of each fatty acid differs. The “parent” fatty acid in each family is metabolized and changed into a “child” fatty acid in the horse’s body. The child fatty acids are the ones that elicit the biological response. For example, the parent omega-6 fatty acid, linoleic acid, is metabolized to arachidonic acid through a series of steps (Figure 1). Arachidonic acid has more biological activity than linoleic acid and is responsible for eliciting stronger inflammatory effects. Similarly, the parent omega-3 fatty acid, linolenic acid, is elongated and changed into eicosapentaenoic acid (EPA). While EPA has some biological activity, it can be further changed into a “grandchild” omega-3, docosahexaenoic acid (DHA), which is responsible for eliciting more subdued inflammatory responses in the body (Figure 1).

Good sources of omega-3 fatty acids include flaxseed or flaxseed oil and fish oils (e.g. menhaden, cod liver, salmon). Of all the oils routinely used in horse feeds, only canola oil has a respectable omega-3 content (Table 1). Therefore, we are somewhat limited as to the source of supplemental omega-3 fatty acids. But, do not forget that forages (hay or pasture) are also a good source of omega-3 fatty acids (Table 1). While forages do not contain a large amount of total fat, they do supply more omega-3 fatty acids than omega-6. And because of the sheer amount of forage horses eat (or should eat), the total amount of omega-3 they supply often surpasses the amount of omega-3 fatty acids that are provided by the level of flax or fish oil typically supplemented.

In our laboratory, we are trying to determine if the source of omega-3 fatty acids influences the horse’s response. The omega-3 fatty acids in flaxseed and oil are predominantly in the form of linolenic acid (the parent). In contrast, the omega-3 fatty acids in fish oil are in the form of EPA and DHA (the child and grandchild). Therefore, if omega-3 fatty acids are supplemented via fish oil, there is less processing that needs to take place by the body to elicit a biological response compared to when flaxseed is used. We have found that supplementing milled flaxseed results in greater omega-3 fatty acids in blood and mare milk than no supplementation, but supplementing an equal amount of omega-3 in the form of fish oil results in greater amounts of omega-3 fatty acids (primarily in the form of EPA and DHA) in blood and in mare milk compared to milled flaxseed. We have also found that markers of immune system function and inflammatory responses were modified by feeding horses fish oil, but not when an equal amount of omega-3 was provided by milled flaxseed. This suggests there may be a limitation in the horse’s ability to convert the parent omega-3, linolenic acid, into the biologically active EPA and DHA. Studies are still needed to determine if this means that flaxseed isn’t as potent a source of omega-3 fatty acids, or that more flaxseed (relative to the amount of fish oil) would have to be fed to elicit a similar response.

We have also learned that by feeding the mare, we can influence the fatty acid content of her milk and the fatty acid content of the foal’s blood, both in utero and after suckling. In addition, the anti-inflammatory effects and immune system modifications conferred by omega-3 supplementation of the mare are also passed along to the foal. Supplementation of the mare with fish oil resulted in greater antibody levels in mare colostrum and foals exhibited a subdued inflammatory response to a challenge with a skin irritant.

Our ongoing studies will address whether it’s the amount omega-3 fatty acids in the diet or the ratio of omega-3 fatty acids to omega-6 fatty acids that is important to elicit a biological response. Although these fatty acids have seemingly opposing actions, the ratio between omega-3 and omega-6 fatty acids may be important for modulating the final response. We have also just completed a study to determine if supplementation of omega-3 fatty acids increases the need for vitamin E in the diet. Omega-3 and omega-6 fatty acids, by nature, are prone to oxidation. While some studies in humans have shown that supplementation with these long-chained fatty acids increases oxidative stress and the need for antioxidants such as vitamin E, more recent research suggests that omega-3 fatty acids may provide some antioxidant activity of their own.

Conclusions
Adding fat to the horse’s diet has been shown to produce many benefits. However, in our sincere effort to provide a safer source of calories than cereal grains, we are learning that the type of fat we feed may influence other biological processes in the body. Omega-3 fatty acids have been shown to positively affect human health by decreasing the inflammatory response and boosting the immune system. Therefore, there is interest in supplementing omega-3 fatty acids in equine diets. While the health benefits of omega-3 fatty acid supplementation have been studied extensively in humans, there is still much work to be done in horses before reasonable recommendations can be given.

Table 1: Fatty acid composition of feeds commonly fed to horses
Feed Total fat Total Omega-6* Total Omega-3* Linolenic* EPA* DHA*
Corn oil 100 % 57 % 2 % 2 % Negligible Negligible
Soybean oil 100 % 54 % 8 % 8 % Negligible Negligible
Canola oil 100 % 21 % 11 % 11 % Negligible Negligible
Flaxseed 40 % 16 % 57 % 56 % Negligible Negligible
Fish oil 100 % 4 % 24 % 2 % 12 % 9 %
Cereal grains 3 % 30 % 3 % 2 % Negligible Negligible
Pasture forage 2 % 15 % 60 % 56 % 2 % 4 %
Hay 3 % 16 % 30 % 27 % < 1 % < 1%
*Percentages of fatty acids are shown as a proportion (%) of the total fat content of the feed.