You've probably heard some talk about omega-3 and omega-6 fats contributing to human heart health. Your horse needs these essential fats in correct amounts too, but first let's take a brief look at fat requirements in general.
Dietary Requirement for Fat
The horse has no actual dietary requirement for fat per se. A horse's natural diet-grass and other plants-is very low in fat. It ranges from 4% to 6% fat, versus around 30% in a "moderate" human diet.
The reason there's no dietary requirement set for fat-as there is for protein, for example-is that the horse can manufacture fats very easily from carbohydrates or amino acids. So can humans. This is how excess calories from any source are converted into fat for storage.
However, horses and people do require dietary intake of two very specific kinds of fat called omega-3 and omega-6 fatty acids. These are called essential fatty acids because it's essential that they be present in the diet since the body can't manufacture them internally. They serve very important, and very different, functions.
The inflammatory response is very important to the smooth functioning of a healthy immune system and defense against diseases. The omega-6 fatty acids are important in generating a vigorous immune response, while the omega-3 fatty acids work to keep the response in check and also protect the immune system from damage.
The Essential Essentials
• The horse's natural diet-plants and grasses-is very low in fat, only between 4% and 6%.
• The horse does require dietary intake of omega-3 and omega-6 fatty acids, because the body can't manufacture them.
• The omega-6 fatty acids help generate a strong immune response, while the omega-3 fatty acids keep the response under control.
For example, endotoxemia is a condition that results when bacterial toxins get into the horse's bloodstream. This typically causes a body-wide severe inflammatory response. Several studies have shown that feeding a source of omega-3 fats can modify the severity of that reaction. Other conditions, such as arthritis and allergies, also have an inflammatory component.
Omega-3 fat is present in plant material as alpha-linolenic acid. Once inside the body, this undergoes conversion to eicosapentaenoic acid (EPA) and then to docosahexaenoic acid (DHA).
When a human or other carnivore/omnivore eats meat or fish, they consume omega-3 fatty acids in the form of EPA and DHA directly, without conversion.
DHA then is further converted to an anti-inflammatory prostaglandin (a signaling molecule that tones down inflammation and blood clotting) and other cytokines (signaling molecules) that are cousins to inflammatory cytokines but have much weaker effects.
The omega-6 fat in plants is alpha-linoleic or gamma-linoleic acid. The alpha-linoleic acid in plant foods is converted to gamma-linoleic in the body and from there to arachidonic acid, which gives rise to cytokines that are involved in inflammation.
Very little research has been done into dietary requirements for these fatty acids in horses. Thanks to a growing interest in "healthy fats" for prevention of heart disease in humans, though, we do know a lot more about what a horse's natural intake would likely be.
Grasses contain anywhere from four to six times as much omega-3 alpha-linolenic acid as they do omega-6 alpha-linoleic acid. This means that a horse would normally take in a much higher level of omega-3s than omega-6s.
Unfortunately, omega-3 fats are very fragile. When grass is cut, the omega-3 content is rapidly lost. The omega-6 fatty acids are a bit more resistant to breakdown. Hay, therefore, is lower in omega-3 compared to omega-6 than fresh grass.
The situation just gets worse if you feed vegetable oils, grains, seeds, or high-fat seed meals. These are also high in omega-6 fatty acids. The only readily available feed ingredient high in omega-3 fatty acids is flaxseed.
A horse on a diet of 100% fresh grass will take in as much as 15 grams/day of the anti-inflammatory omega-3 fatty acids and about a quarter as much omega-6 fats. Horses on diets of hay and grain (plus seeds and brans) will have a reversed ratio-more inflammatory omega-6 than omega-3 fatty acids.
Diets higher in omega-6 fats than omega-3 fats can interfere with the use of what omega-3 fats the horse has available. This is because the enzyme that starts the plant fatty acids on their pathways inside the horse is the same for both linoleic as linolenic acid. And when one type of fatty acid is present in excess of another, it can monopolize or "hog" that enzyme. (See the chart on page 49.)
The Bottom Line
Supplementing to keep the ratio of your horse's intake of essential omega-3 and omega-6 fatty acids in amounts and proportions similar to those in fresh grass seems wise. Flaxseed remains the best way to accomplish this. Feed between 2 and 4 ounces per day (use higher amounts for horses on grain) of either freshly ground whole flaxseeds or an equine ground stabilized flax supplement.