Q: My 18-year-old trail horse has metabolic issues but works heavily, covering up to 30 miles each week over uneven terrain. I switched him to low-nonstructural-carbohydrate feed and hay at the recommendation of his nutritionist but, when he quickly started losing weight, we added a fat supplement to his diet. Why is fat safe for him even though he has metabolic problems?

A: Equine metabolic issues can be challenging, so it is great you work with a nutritionist. Equine metabolic syndrome (EMS) impacts the horse’s ability to metabolize sugars. Horses with EMS have abnormally high levels of insulin in their blood, which results from their cells not responding to the hormone adequately.

When a metabolically normal horse eats a meal high in nonstructural carbohydrates (NSCs), his body sends glucose into the bloodstream, referred to as the glycemic response. This triggers the pancreas to release insulin, which signals certain body cells to take up glucose and store it as glycogen the horse can use for energy.   

Metabolic horses’ cells do not respond properly to the insulin—termed insulin resistance—and the pancreas continues secreting it. Insulin resistance results in hyperinsulinemia (elevated insulin levels).

When managing metabolic horses’ diets, the goal is to reduce their glycemic response to ensure blood insulin levels do not become too high. Owners usually accomplish this by reducing NSCs in the diet. When a metabolic horse is not overweight, equine nutritionists often recommend adding a fat source to increase calories without elevating NSC content.

Fats, or lipids, are great energy sources for horses. In fact, fats provide more than double the energy carbohydrates do, pound for pound, but they do not cause a spike in blood insulin levels.

Horses do not have a gallbladder but can still digest and utilize fat effectively. The liver produces and releases bile into the small intestine, where it emulsifies the lipids to start digestion. Once the small intestine finishes digesting the fat, it enters the bloodstream, where it can be transported to the liver, muscles, adipose tissue (body fat), or other parts of the body as needed.

When adding fat to your horse’s diet, be cautious and always add it slowly to give him time to adapt to the change. Common fat sources include camelina oil, flax oil, ground flax, ahiflower oil, and fish oil. Work with a qualified equine nutritionist to determine which is best for your horse.

Take-Home Message

Ensure your metabolic horse consumes a diet low in NSCs, and if he needs additional energy, consider adding a fat source, but do it gradually. Continue to work closely with your equine nutritionist so your horse receives the right amount of fat in his diet to meet his individual needs.

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