You’ve probably heard about the health benefits of omega-3 fatty acids from fish oil, but does this supplement work for horses?

Fish oil is often added to diets, both human and animal, as a source of the essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

These two omega-3’s have gained a lot of attention because they can promote beneficial physiological changes in horses including: [1]

  • Improved skin and coat quality
  • Reduced inflammation
  • Weight management
  • Support for joint health
  • Improved respiratory health

Omega 3’s are a type of long-chain poly-unsaturated fatty acid (PUFA) that play an important role in equine physiology. Compared to pro-inflammatory omega 6’s like linoleic acid (LA), omega 3’s have an anti-inflammatory effect within the horse’s body.

If your horse’s diet is too high in omega 6’s, feeding fish oil could improve the omega 3:6 ratio and support a healthy inflammatory response. However, some question whether horses should be fed fish oil because they are herbivores and would not naturally eat fish.

Should You Give Fish Oil to your Horse?

Horses naturally obtain another omega-3 fatty acid – alpha linolenic acid (ALA) – from their forages and grains like flaxseed. But in order to have a beneficial effect, ALA must first get converted into EPA or DHA.

Horses can convert ALA to DHA and EPA, but this process is inefficient and does not produce sufficient DHA and EPA to confer the purported health benefits. For this reason, directly supplementing the equine diet with DHA and/or EPA is preferable.

Feeding your horse fish oil is one way to supplement their diet with DHA and EPA. Compared to plant sources which contain minimal or no DHA and EPA, fish oil is rich in these beneficial fatty acids and provides a favourable ratio of omega-3 to omega-6 fats.

However, fish are not naturally a part of the equine diet and fish oil can have a strong odor which raises palatability issues for some horses. Fish oil also has a higher cost per serving compared to other fat sources used in the equine diet.

Other marine sources, such as microalgae, are an alternative that provide high levels of DHA without the adverse odor. Microalgal DHA can be top-dressed on the horse’s feed with minimal palatability concerns.

Mad Barn’s W-3 oil provides 1,500 mg of microalgal DHA and 1,000 mg (1,500 IU) natural vitamin E in a typical serving. This supplement is a good choice for horses that require more energy in their diet to support exercise performance or healthy weight gain.

As with all dietary changes, we recommend consultation with an equine nutritionist to determine what is best for your horse. You can submit your horse’s diet and one of our equine nutritionists will provide a complementary assessment.

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Effects of Fish Oil in Horses

Feeding DHA and EPA can support numerous benefits in horses, including promoting skin and coat health, enhancing joint comfort and improving performance.

Fat is a denser energy source compared to carbohydrates and is metabolized more efficiently. Fat is considered a “cool” energy source, as it has a lower heat of digestion compared to protein and doesn’t promote hot or reactive behavior like starches/sugars.

Before we consider the known palatability issues of fish oil, let’s take a look at the proposed benefits of fish oil supplements in horses.

Improved Exercise Performance

In one study, 10 horses (a mix of Thoroughbreds and Standardbreds) were given either fish oil (containing 8% DHA and 10% EPA) or corn oil (containing 0.3% DHA and 0.05% EPA). The oils were given at a rate of 324 mg per kg of body weight for nine weeks. [3]

The horse’s daily exercise intensity increased over the nine-week period, leading to a final exercise challenge day when horses were assessed while at a moderate gallop on a treadmill.

During exercise, horses receiving fish oil had a lower heart rate suggesting better exercise tolerance. These horses also had a higher ratio of glucose to insulin, which indicates better insulin sensitivity compared to the horses fed corn oil.

Lactate, which is produced by muscles during exercise and can cause muscle fatigue, was not affected by treatment either during or after exercise.

Horses receiving fish oil had lower levels of glycerol and free fatty acids in their blood, suggesting they were not mobilizing as much fat from their adipose tissue.

By relying less on the release of fat from adipose tissue, horses fed omega-3s might not deplete their energy reserves as quickly and may be able to sustain longer periods of exercise.

Fish oil can improve insulin sensitivity and exercise tolerance in performance horses.

Anti-Inflammatory Effects

Omega-3 fatty acids have been consistently shown to reduce inflammatory markers in humans and animals.

In mature mares at maintenance, diets that contained fish oil (3% of the total diet) resulted in lower levels of inflammatory markers compared to corn oil. The researchers evaluated lung cells taken during bronchoalveolar lavage, a test that is commonly used to diagnose inflammatory airway disease in horses.

They found that lung cells taken from horses given fish oil supplements produced lower levels of pro-inflammatory factors. [4]

This suggests that horses with recurrent airway obstruction or other chronic inflammatory diseases might benefit from omega-3 supplementation to attenuate the exaggerated immune response.

Cardioprotective Effects

Omega-3 fatty acids are thought to support heart health and improve circulation by lowering the levels of fat (lipids) and cholesterol in the blood. Excess lipids in the blood can exacerbate clogged arteries leading to heart disease.

Exercising horses given fish oil had lower levels of triglycerides (fat) and cholesterol in the blood compared to horses given corn oil. [5]

High cholesterol and triglyceride concentrations can contribute to cardiovascular disease and are one of the reasons why fish oil and EPA/DHA are known to play a cardioprotective role in humans. [1]

Improved Sperm Quality

The omega-3 fatty acids DHA and EPA support antioxidant status in seminal fluid which helps keep sperm healthy.

One of the main challenges with cooling and storing sperm from stallions is the viability after storage. Boosting antioxidant status and health of sperm could result in improved viability.

Miniature Caspian stallions were supplemented with fish oil at an inclusion rate of 2.5% of their diet (on a dry-matter basis). This would be equivalent to 250 grams per day for a horse consuming a typical 10 kg of dry matter. [6]

After 60 and 90 days of supplementation, sperm concentration was significantly higher compared to non-supplemented horses. Importantly, when they looked at sperm after 24 and 48 hours of storage, motility and viability were greater in horses supplemented with fish oil.

Drawbacks of Fish Oil

Although there are clear benefits provided by the supplementation of fish oil in a horse’s diet, there are some drawbacks to horse owners:

  1. Cost
  2. Palatability
  3. Consistency and sustainability

Some fish oil products have a strong smell and some horses will not readily consume it. Compared to fish oil, oils derived from plant sources are both more palatable and more cost-effective.

However, most plant oils contain no EPA or DHA and will not provide the same benefits seen with fish oil. An exception is microalgae-enriched oils which do contain supplemental DHA.

Fish oils for animal consumption can come from a variety of sources, not all of which have high levels of DHA and EPA. Some fish oils might also have contaminants like lead and mercury which may or may not be disclosed on the product label.

Environmental concerns such as declining global fish stocks and by-catch might also factor into your decision to feed fish oil to your horses. There is also a concern regarding peroxidation and product freshness as fats that are oxidized can be harmful to feed.

These concerns can be mitigated by sourcing high quality equine fish oil supplements, but beware the potentially higher cost per dose.

Microalgal DHA for Horses

Innovations in human nutrition have provided unique sources of DHA and EPA for vegans and vegetarians who do not wish to consume animal products. These sources can also be added to the equine diet.

Microalgal DHA is derived from algae grown in controlled facilities which minimizes environmental impact and results in a pure, consistent product without risk of contaminants.

Oils derived from marine microalgae, like LG-MAX from Alltech, have high levels of DHA. [7] This is the type of algal DHA that you will find in Mad Barn’s W-3 oil supplement.

Research shows that horses fed algal oil and fish oil had higher levels of EPA and DHA in muscle compared to horses given flaxseed oil [9].

When levels of EPA and DHA are higher in the body, this results in improve fluidity of cell membranes. Greater cell membrane fluidity means cells of many different types can respond better to a variety of signals such as hormones, oxidative damage and immune responses.

Because this is a newer source of DHA, research on microalgal DHA in horses is limited. However, several studies demonstrate benefits in horses:

Equine Metabolic Syndrome

The anti-inflammatory effects of DHA are beneficial to horses with Equine Metabolic Syndrome (EMS), a condition associated with chronic inflammation.

Horses diagnosed with EMS were given either microalgal DHA (16 grams per day) or a placebo. After 46 days, horses given DHA had lower levels of the pro-inflammatory marker TNF-alpha.

During this period, control animals developed worsening insulin responses whereas the DHA supplemented horses showed no change. [8]

The anti-inflammatory effect of microalgal DHA might protect EMS horses from worsening insulin sensitivity.

Insulin Regulation

Insulin resistance is a hallmark of equine metabolic syndrome, characterized by the body’s failure to respond to insulin appropriately.

In one study, researchers directly measured the effects of microalgal DHA on insulin sensitivity. The researchers induced insulin resistance in healthy horses by administering dexamethasone.

Dexamethasone is a commonly used corticosteroid drug given to horses with respiratory issues, chronic allergies, or arthritis. A known side effect of dexamethasone is insulin resistance with prolonged use.

Researchers fed the horses either 150 grams of DHA-rich microalgae per day or a control diet for 21 days. After the 21 days, the horses given microalgal DHA had lower levels of blood sugar (glucose) and insulin and better ratios of insulin to glucose.

These results suggest that horses fed DHA have improved insulin sensitivity compared to those on control diets. [10]


Dysbiosis, an imbalance in microbial populations in the horse’s hindgut, is common in horses fed high-starch diets and/or during stressful circumstances such as trailering and competition.

Dysbiosis can impair fibre digestion, nutrient absorption and gut motility leading to increased risk of hindgut ulcers or other immune challenges.

Feeding microalgal DHA could shift the intestinal microbial population in a favourable way and help maintain gut health even on high-starch diets.

In one study, horses were fed either a high-fibre (hay only) or high-starch (44% barley) diet and were given either a combined yeast and microalgal DHA supplement or no supplement. The diets were fed for 3-4 weeks. [11]

The high-starch diet predictably decreased the number of microbial species and diversity in the horse’s cecum and colon. There was a particularly large decline in the cellulose (fibre) digesting bacteria. This result was observed regardless of whether the horses were given yeast and microalgal DHA or not.

The researchers also evaluated the levels of specific beneficial microbial strains that are known to support hindgut health. Yeast and microalgal DHA supplementation on a high-starch diet restored levels of beneficial Bacteriodetes in the colon to levels that were found when horses were given high-fibre diets.

This study suggests that the combination of microalgal DHA and yeast could support fibre-digesting capacity and minimize dysbiosis in the hindgut as horses transition from high-fibre to high-starch diets.

Microalgal DHA can support fibre digestion and provide a dense energy source in place of grain to maintain a healthy hindgut.


Joint inflammation can cause pain and lameness in horses leading to poor performance and mobility.

In one study, horses were fed either a control diet or the control diet plus 190 grams per day microalgal DHA for 60 days. [12] Short-term joint inflammation was then induced by injecting the inflammatory agent lipopolysaccharide (LPS) into the medial carpal joint of horses.

Horses given microalgal DHA had lower lameness scores 12 hours after LPS injection compared to horses on the control diet. They also did not experience a rise in heart rate or pro-inflammatory markers after the injection, in contrast to horses on the control diet.

This study suggests that dietary microalgal DHA can mitigate joint inflammation and improve comfort in horses with joint health issues.

Microalgal DHA can improve comfort and minimize inflammation in horses with joint pain.

Alternatives to Fish Oil for Horses

How do other sources of omega-3 fatty acids compare to fish oil for horses? Various plant oils have also been used to supplement essential fatty acids in horses.

Flax, canola oil, soybean oil, rice bran, corn oil, and camelina oil have all been used to add fat to equine feeding programs. Of these, flaxseed oil and camelina oil have the highest content of the omega-3 fatty acid ALA.

However, none of these plant oils provide EPA or DHA directly. Instead, the ALA found in these fat sources must be converted to EPA or DHA by enzymes in the horse’s body. As mentioned previously, this conversion rate is poor and will not raise levels of EPA or DHA enough to promote a significant physiologic benefit.

That’s why you may want to consider a DHA-enriched oil like our w-3 Oil blend instead.

W-3 Oil

Mad Barn’s W-3 oil is one of the only equine supplements that contains algal sources of DHA which horses find far more palatable than fish oil.

W-3 oil contains a unique blend of marine algae, soybean and flax oil at a low cost without the fishy smell or taste.

A typical serving size for horses at maintenance (100 mL for a 500kg horse) provides 1500 mg of DHA and 1000 mg (1500 IU) of natural Vitamin E.

W-3 oil can also be fed to support healthy weight gain for hard keepers by increasing the serving size to 200 mL per day.

To determine whether this supplement would be appropriate for your horse, you can submit your horse’s diet for a complementary analysis by our equine nutritionists.

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  • Promotes joint comfort
  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3's

Soybean oil

Soybean oil is used in the equine diet as a fat source and contains both omega-3s and omega-6s.

The most abundant fatty acid in soybean oil is linoleic acid, an omega-6 fatty acid. If long-term use is intended, the ratio of omega-3 and omega-6 fatty acids in the whole diet should be evaluated. Equine nutritionists typically aim to keep this ratio within 1:4 and 1:6 omega-3 to omega-6 fatty acids.

Soybean oil is highly palatable and a cost-effective way to add energy to a horse’s diet to support weight gain.

Flaxseed oil

Flaxseed oil contains a large amount of ALA, the precursor to DHA and EPA. Flax oil provides a more favourable omega-3 to omega-6 ratio of 1:2, compared to soybean oil which has a ratio of 1:10.

Research has shown that supplementing horses with flaxseed oil significantly increases plasma EPA but not DHA concentrations [13].

One study examined the effects of feeding soybean oil or flaxseed oil at a rate of 25 mL per 100 kg body weight. Horses receiving flaxseed oil had lower plasma glucose and cholesterol levels compared to those fed soybean oil.

They also had higher antioxidant capacity with more active antioxidant enzymes and higher levels of antioxidant compounds. [14]

Ground flaxseed can easily be added to the horse’s diet. In addition to beneficial fatty acids, ground flax also supplies proteins, vitamins and minerals.

Horses with recurrent seasonal skin allergies (sweet itch) that were given 1 lbs of ground flaxseed per day had smaller skin lesions in response to allergens from insect bites compared to horses on a control diet. [15]

Camelina Oil

Camelina oil is derived from the Camelina sativa plant, also known as false flax.

It has a lower omega-3 content than flaxseed oil (39% for camelina oil, 54% for flaxseed oil) and a lower ratio of omega-3 to omega-6 fatty acids. It also contains four times less ALA than flaxseed oil.

One benefit of camelina is that it is a natural source of small levels of Vitamin E. Dietary oils that contain vitamin E have improved shelf life because this vitamin protects against lipid peroxidation (oxidative damage to the fats).

Per 100 ml of product, camelina oil provides 150 IU of Vitamin E whereas flaxseed oil contains 26 IU. In contrast, Mad Barn’s W-3 oil contains 1,500 IU of natural vitamin E (10x higher than camelina oil).

At this level, it not only extends the shelf-life of the oil but can also be a useful vitamin E supplement for horses.

Camelina oil contains a lower concentration of omega-3 fatty acids compared to flax oil, but provides small amounts of Vitamin E.

How to Feed Oils to Horses

Total fat in the equine diet should not exceed 8%, taking into account the fats in forage, pasture, grains and supplements.

All fats will provide the same amount of calories (9 kcal per gram of fat), but the fatty acid composition can differ greatly which could affect the horse’s health.

To determine how much fat to add to your horse’s diet, you can submit their feeding program for analysis and our equine nutritionists can help you make any desired changes.

How Much Oil Should You Feed Per Day?

The exact amount of supplemental oil to feed your horse depends on a number of individual factors including your horse’s current diet, bodyweight, health status and workload.

However, we can use protocols from the studies mentioned above to estimate an effective dose for horses. Some of the studies demonstrated beneficial outcomes when the horses were supplemented at a rate of 320 mg/kg bodyweight.

For a 500 kg horse, this would be 160 mg of oil per day. The concentration of fat in the specific product you are feeding will determine the volume (mL) of product to give to your horse.

Other researchers supplemented at 2.5-3% oil on a dry matter basis. For an average horse consuming approximately 10 kg of dry matter per day, this amounts to approximately 250 – 300 mg of oil.

A good starting range for introducing oil to your horse’s diet would be 100 – 200 mL per day. Horses that are easy keepers or overweight may need to use a lower dosage to avoid weight gain.

How to Introduce Oil to your Horse’s Diet

The most important thing to remember when introducing a new feed to your horse’s diet is to do so slowly.

A general rule of thumb is to start with 1/4 cup or 60 mL of oil and gradually add 60 mL more every 2-3 days until you reach the desired amount.

Fat is a readily available source of energy and highly digestible. Caution should be used when adding fats to a sedentary horse’s diet, as weight gain is possible.

If you have an exercising horse who has trouble maintaining weight, the addition of oil may aid in weight gain and maintenance.

Which Equine Oil Supplement to Choose?

Based on the presented studies, a few conclusions can be drawn to help you determine which source of supplemental oil you should add to your horse’s diet.

Joint Care and Antioxidant Protection

If you have a performance horse or a senior horse with arthritis, then reducing inflammation may be one of your biggest concerns.

Marine oils, like fish oil and algal oil that are high in DHA and EPA would be the best option to support anti-inflammatory processes. [2] [3] [4]

When exercising, horses produce a lot of oxidants that can cause damage to their cells and slow recovery. Flaxseed oil has been shown to increase plasma antioxidant concentrations and could be a cost-effective option for exercising horses that are slow to recover after exercise but may or may not have joint health issues. [14]

Senior horses with arthritis may see improvements when supplementing omega-3 rich oils like W-3 oil. However, excessive weight gain should be carefully avoided to minimize load on their joints and to support overall health.

For senior horses, it is especially important to evaluate your horse’s diet before making changes to make sure you are supporting healthy aging. Other aspects of their diet may need to be adjusted to lower caloric intake while still getting the benefits of fatty acids.

Allergies and skin/coat quality

If you have a horse struggling with poor skin and coat quality, dermatitis, or sweet itch, any oil with a greater omega-3 content will likely improve coat quality.

Researchers in Malaysia reported that increasing omega-3 levels in blood was positively correlated with skin and coat health. [16]

Oils with high levels of omega-3s will likely achieve the greatest benefit for skin allergies and coat quality, including flaxseed oil, fish oil and microalgal DHA.

Pleasure Horses

For pleasure horses that are mostly sedentary, omega-3 fatty acids can have beneficial health effects. However, the diet needs to be carefully evaluated to minimize weight gain, particularly in older easy keepers.

An equine nutritionist can help you ensure your horse’s feeding program is not providing too many calories while still favouring a beneficial balance of essential fatty acids.

Oils that contain a high level of omega-3s with lower levels of other fats are a good option because their inclusion rate will be lower so you don’t end up feeding too much fat.

Dense oils such as fish, flaxseed, or W-3 oil are the best options for pleasure horses.

In summary, supplemental oils with higher amounts of omega-3s, specifically DHA and EPA, have been shown to improve immune function, skin and coat health, inflammation, and performance during exercise. Fish oil is one option, but it is not the only option for adding more DHA and EPA to your horse’s diet.

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  1. Narayan,B. et al. Physiological effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) – A review. Food Reviews Int. 2006.
  2. Manhart, DR. et al. Markers of Inflammation in Arthritic Horses Fed Omega-3 Fatty Acids. Professional Anim Sci. 2009.
  3. O’Connor, CI. et al. The effect of dietary fish oil supplementation on exercising horses. J Anim Sci. 2004. View Summary
  4. Hall, JA. et al.Effect of type of dietary polyunsaturated fatty acid supplement (corn oil or fish oil) on immune responses in healthy horses. J Vet Intern Med. 2004. View Summary
  5. O’Connor, CI. et al. Dietary fish oil supplementation affects serum fatty acid concentrations in horses. J Anim Sci. 2007. View Summary
  6. Kheradmand Garmsir, A. et al. Effects of Dietary Thyme (Thymus vulgaris) and Fish Oil on Semen Quality of Miniature Caspian Horse. J Equine Vet Sci. 2014.
  7. Lum, KK. et al. Dual potential of microalgae as a sustainable biofuel feedstock and animal feed. J Anim Sci Biotech. 2013.
  8. Elzinga, SE. et al. Effects of Docosahexaenoic Acid-Rich Microalgae Supplementation on Metabolic and Inflammatory Parameters in Horses With Equine Metabolic Syndrome. J Equine Vet Sci. 2019. View Summary
  9. Hess, TM. et al. Effects of two different dietary sources of long chain omega-3, highly unsaturated fatty acids on incorporation into the plasma, red blood cell, and skeletal muscle in horses. J Anim Sci. 2012. View Summary
  10. Brennan, KM. et al. Effects of a docosahexaenoic acid–rich microalgae nutritional product on insulin sensitivity after prolonged dexamethasone treatment in healthy mature horses. Am J Vet Res. 2015.
  11. Grimm, P. et al. Dietary composition and yeast/microalgae combination supplementation modulate the microbial ecosystem in the caecum, colon and faeces of horses. Br J Nutr. 2020. View Summary
  12. Brennan, KM. et al. The effect of dietary microalgae on American Association of Equine Practitioners lameness scores and whole blood cytokine gene expression following a lipopolysaccharide challenge in mature horses. J Anim Sci. 2017.
  13. Hansen, RA. et al. Effects of dietary flaxseed oil supplementation on equine plasma fatty acid concentrations and whole blood platelet aggregation. J Vet Intern Med. 2002. View Summary
  14. Sembratowicz, I. et al. Effect of dietary flaxseed oil supplementation on the redox status, haematological and biochemical parameters of horses’ blood. Animals. 2020. View Summary
  15. O’Neill, W. et al. Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Can J Vet Res. 2002. View Summary
  16. Goh, YM. et al. Plasma N-3 and N-6 fatty acid profiles and their correlations to hair coat scores in horses kept under Malaysian conditions. J Vet Malaysia. 2004.