What Hay is Safe for My EMS Horse?

An equine nutritionist explains why NSCs, ESCs, and WSCs are important factors to consider when choosing hay for your EMS horse.
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two horses eating grass hay
It is important to understand your metabolic horse’s sugar intake. | iStock

Q. My horse was diagnosed with equine metabolic syndrome (EMS) and the hay I have is higher than 10% in nonstructural carbohydrates (the recommended, safe level for EMS horses)—but only slightly. Can you explain what this value means and how ethanol-soluble carbohydrates (ESC) and starch play a part in the equation? Could my forage be safe for my EMS horse after all­­?

A. This is a great question because understanding your metabolic horse’s sugar intake is a key step in developing a supportive nutrition program. The important thing to understand is the difference between ethanol-soluble carbohydrates (ESC), water-soluble carbohydrates (WSC), and nonstructural carbohydrates (NSC).

Ethanol-soluble carbohydrates are essentially simple sugars and have a direct impact on blood glucose levels. Water-soluble carbohydrates include both the simple sugars and fructans (the primary storage carbohydrate in cool-season grasses); however, when calculating NSCs you can add WSC and starch (the primary storage carbohydrate in legumes and warm-season grasses) values together but recognize that fructans do not play a direct role in blood glucose and insulin levels.

Microbes in the horse’s hindgut ferment fructans. This results in lactic acid production and, when a buildup of lactic acid occurs, the pH of the hindgut environment drops. This change in the environment negatively impacts the microbes, and many might die off. When this happens endotoxins are released into the bloodstream, which can cause laminitis. Therefore, fructans can play a role in laminitis but, if you are most concerned about blood insulin levels, it might be acceptable to exclude fructans from the calculation.

The most up-to-date recommendations suggest calculating hydrolyzable carbohydrates (HC), which is the calculation of ESC plus starch. The fructans are not included because they are not directly related to a high glycemic response. That being said, if you have a horse that is struggling with laminitis, it is best to avoid any potential triggers, including fructans.

Likely the most important consideration is that the 10% NSC recommendation is simply a guideline. Just because a hay is low in ESC and starch does not mean your horse will not have issues with it. For example, some metabolic horses might be on a diet that is 14% HC and never have issues, whereas others might need less than 8%. It is truly individual; keep this in mind when you are designing a feeding and management program for your metabolic horse.

When choosing a hay for this horse, you will want to test the hay to ensure that the ESC + starch is less than 10% on a dry matter basis. Normally these horses will do quite well on a grass or grass mix hay that is mature. If the hay you can source is too high in sugar content, soaking can be an option. However, the climate you are in can limit this as a practical year-round option if temperatures are freezing. When soaking hay, it should be completely submerged in water for 60 minutes if in cold water, or 30 minutes in warm water.

The other key consideration is the amount of hay you should be feeding your horse. Free-choice hay is fantastic, unless it results in obesity. Many metabolic horses tend to be overweight so reducing their hay intake and using slow feeding tactics might be necessary. If your horse is sound, increasing movement is another positive way to promote weight loss.

When a horse is overweight and needs to lose weight, equine nutritionists recommended feeding hay at a rate of 1.5% of their body weight. It is not recommended to reduce their hay intake below this amount. For a 500 kg (1,100lb) horse this is about 7.5 kg (16.5 lbs). If the horse is not overweight, feeding at 2% of their bodyweight is the usual recommendation. However, remember that each horse is individual so if you are unsure, check with your veterinarian or nutritionist.

Overall, understanding the sugar content of your metabolic horse’s diet is a crucial part of management, but remember it is simply a guideline. When dealing with a history of laminitis, always follow your veterinarian’s recommendations and consult a qualified equine nutritionist if you are looking for help with an optimal diet plan.


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Written by:

Madeline Boast, MSc completed her master’s in Equine Nutrition at the University of Guelph and started an independent nutrition company known as Balanced Bay. She has worked with a variety of equids—from Miniature Ponies to competing Thoroughbreds. Boast designs customized balanced nutrition plans that prioritize equine well-being, both for optimal performance and solving complex nutritional issues and everything between. 

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