This article from The horse.com is the clearest explanation of what we test and why
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.
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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