Q.My horse recently had a severe case of hives that my veterinarian is attributing to contact dermatitis (likely an allergy to tree pollen). She has recommended adding an omega-3 supplement to help support his immune system. I currently feed my gelding hay and the manufacturer’s minimum recommended serving of a concentrate. Will adding an omega-3 supplement make his diet imbalanced? Is it possible to find a concentrate that has enough omega-3s without additional supplementation? And, what’s the recommended dosage of omega-3s for horses with allergies?

—Via e-mail

A.Dealing with hives and allergies can be frustrating for both you and your horse. Omega-3 fatty acids are often recommended for horses prone to allergies. They are essential nutrients meaning that they must be present in the horse’s diet, which is also true of omega-6 fatty acids.

The overall response of normal biological functions to these fats is impacted by their relative proportion. Research has shown that feeding different amounts of these essential fatty acids can change their contributions to cell membranes. In turn this can impact cell membrane integrity as well as such functions as protein synthesis and receptor signaling. This is how these fatty acids might impact allergic responses. Omega-3 fatty acids are often recommended for situations such as allergies because, when incorporated in to cell membranes, they tend to result in weaker inflammatory responses than omega-6 fats.

While a horse’s natural diet of fresh grass is not particularly high in fat (2 to 4%), the fat that’s present is relatively high in omega-3 fatty acids (as much as 55%). Therefore, horses grazing good quality pasture for the majority of the day will consume quite large quantities of omega-3 fatty acids in the form of alpha-linolenic acid (ALA).

Why Are Horse Diets Usually Higher in Inflammatory Omega-6 Fatty Acids?

Omega fatty acids aren’t particularly heat-stable, meaning the quantity in hay is considerably less than in grass. However, the amount of omega-3 is still greater than that of omega-6. That changes when we feed horses grains, which are are naturally higher in linoleic acid (LA, an omega-6 fat). It’s therefore possible that horses fed hay and concentrate feeds are consuming more omega-6 than 3. This is especially true when using high-fat concentrate feeds, because the vegetable oils (soy, canola, corn, etc.) used in such feeds tend to be very high in omega-6 fat.

Adding a specific omega-3 supplement to your horse’s diet will not cause the diet to become unbalanced, but it might shift the balance of omega fats in the diet towards a reduced inflammatory response. While there are manufacturers that add sources of omega-3 fatty acids to their feeds, the amounts might not be great enough to have a positive effect for a horse having such a large inflammatory reaction such as your horse’s hives. This is especially true if the feed also contains omega-6 fat sources.

What Feed Sources Provide Omega-3 Fatty Acids?

Most commercial feeds include plant-based sources of omega-3 such as flax, which provides ALA. Ultimately the horse needs to elongate this form of omega-3 from 18 carbons to 20 carbons to form eicosapentaenoic acid (EPA) and docosaheaenoic acid (DHA). This requires elongase and desaturase enzymes. While we know that horses have these enzymes because EPA and DHA are found in horses that are not directly fed these forms of fatty acid, researchers haven’t confirmed how well they do this or quantified the relative activities of the necessary enzymes in horses. Therefore, while plant-based sources of omega-3 are excellent supplements for the average horse, they might not be enough for a horse suffering from significant inflammation.

Ultimately it’s the EPA and DHA that is being incorporated into and having impacts on membrane function, therefore it’s worth considering when supplementing omaga-3 fatty acids to horses suffering from inflammatory reactions providing sources of EPA and DHA. EPA and DHA sources are limited and the most common supplemental sources are algae or fish oil. Algae provide predominantly DHA, while fish oil provides both EPA and DHA.

How Much Omega-3 Supplementation Do Horses Need?

The quantity of omega-3 fatty acids necessary for is still up for debate. We aren’t even clear on the amount needed for an average healthy horse let alone one suffering from an allergic response. The National Research Council provides an estimate for the daily requirement for LA but doesn’t provide an ALA estimate. However, based on work in other species veterinarians and nutritionists have suggested that the daily intake of omega-6 to 3 (LA:ALA) should be somewhere between a 5:1 to 10:1 ratio.

Limited studies exist in horses looking at the effect of fatty acids on immune function, and their results are mixed. Typically, the amounts of omega-3 supplementation depend on the source. Some examples of amounts recommended by manufactures of straight omega-3 supplements include from between 30 and 60 milliliters of fish oil (6.75 to 13.5 grams EPA and DHA), about 15 to 25 grams of ALA from plant sources such as flax or camelina, or 5 to 10 grams of algae (0.85 to 1.7 grams DHA).

Take-Home Message

Feeding a source of supplemental omega-3 fat to your horse might very well help with inflammatory response being experienced due to allergies. It has been my experience that the positive impacts are greatest if such supplementation is started well before the horse experiences the allergen. While this can be hard to implement for some allergens, certain more seasonal allergies are easier to predict and prepare for. Alternatively, feeding at least a plant-based form of omega-3 supplement year-round is often a good idea.