You’re at the feed store looking for a suitable carrier for the supplements for your horse. The choices are overwhelming. You notice that there are several feed choices that appear to be suitable for your horse, but one is listed as having 12% minimum fat, while the other has 14% minimum fat. That seems high, but you wonder what the implications are.
◆︎ The horse’s diet:
Feral horses have a diet of forages. They are designed to be continual grazers. Their diet consists of grasses, legumes, with the occasional branches and leaves. A grass diet has a fat content of about 2-3%.
Horses do not have a gall bladder. In humans, a gall bladder stores bile, which gets dumped into the intestines to emulsify fats, allowing for absorption. Horses don’t have a gall bladder to dump bile into the intestines. Instead, bile is continually trickled into the intestines to emulsify the small amount of fats in the grasses.
When we feed a bucket containing a large amount of fat, the bile produced becomes overloaded and the oil that has not been emulsified bypasses normal digestion and gets dumped in the hind gut. This may be problematic in that it coats the fibrous forage and potentially inhibits fiber fermentation.
◆︎ Added fat:
When we add fat to our horse’s diet, it usually is in the form of corn oil, soybean oil, or similar. These are high in Omega 6s fatty acids, with only about 1% of the corn oil consisting of omega 3s. Grass, on the other hand, is very rich in omega 3s, with an omega 3 to omega 6 ratio of about 4:1. This is fundamentally important because the over-abundance of omega 6 fatty acids creates a proinflammatory environment, while increasing omega 3s help make that environment anti-inflammatory.
◆︎ Metabolism of fat:
Fat that is absorbed in the small intestine gets taken up by the muscle cells, gets transported to the mitochondria, to create ATP. While at first glance, this may seem to be beneficial, there can be issues with utilizing fat as a significant source of energy.
With added fats to the diet, your horse may have elevated levels of circulating free fatty acids. These compete with glucose for the creation of energy in the cell. When cellular uptake of free fatty acids occurs, it inhibits uptake of glucose into the muscle cell. This can worsen insulin resistance. It has also been documented that excessive fats can actually cause insulin resistance.
◆︎ PSSM horses
This creates a unique problem for horses with muscle disease. Horses with PSSM can benefit from a high fat diet because it provides an alternate source of energy. By utilizing free fatty acids for energy, it bypasses the defective carbohydrate/glycogen metabolism. However the paradox is that by increasing the free fatty acids, the cellular signaling is disrupted and actually creates insulin resistance.
◆︎ Fatty acid oxidation:
Another issue that occurs is that fatty acid oxidation generates a significant amount of reactive oxygen species (ROS). This creates a need for antioxidants to neutralize the free radicals. This can deplete the amount of vitamin E in the body, as well as any other anti-oxidants that the horse may consume. When significant, this could cause muscle soreness and delayed recovery after exercise.
◆︎ Who benefits from added fat:
So which horses could benefit from added fat?
While there seems to be a lot of evidence as to why you would NOT want to supplement fat, there are horses that may benefit:
☛ Hard keepers and/or senior horses: This is a way to increase the caloric intake without relying on grains.
☛ Endurance horses: These horses have a large metabolic need, which is not easily met with forage alone.
☛ PSSM horses: While a high fat diet can cause insulin resistance in these horses, it also has a place to provide energy to the horse – especially when carefully monitored.
◆︎ Which horses should additional fat be minimized or avoided?
If you have a horse that is already insulin resistant, and/or laminitic, you may want to avoid relying on added fats for management.
Additionally, if the horse is overweight, the additional calories from fats may be contraindicated.
◆︎ What type of fats to add:
Most horses on hay diets do not get sufficient omega 3s. The anti-inflammatory effects of the omega 3s may be helpful. This can be added through flaxseed oil, ground flax, camelina oil, or chia seeds.
◆︎ What type of fats may not be helpful:
Added fat from corn oil or soybean oil may not be helpful to your horse. It also depends on the amount of oil that is given. For instance, a few ounces would not be as detrimental to your horse as cups.
◆︎ Parting thoughts:
Horses were designed to be continual grazers. However, due to our horse husbandry practices, it is not possible for a horse to be kept as they have evolved. Being aware of the fats in the feed bag is a part of good horse keeping practice.
We do the best we can for our horses. Understanding our horse's needs is a part of that.
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Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.
©Joan Kulifay, MSc. 2026