Finding the NSC content of your horses hay can help you make educated decisions on the rest of his diet. | The Horse StaffMany horse owners use the term low-starch diet in reference to a concentrate-free diet, a diet safe for laminitic horses, or a low-carb diet. But Jyme Nichols, PhD, director of nutrition for Bluebonnet, says the term has no meaning.There is no real legal or regulated definition for low starch, said Nichols during her presentation at the 2026 EquiSUMMIT Equine Nutrition & Health Conference, hosted by Kemin Industries. The only legal requirement for a company to market a low-starch feed is that the company must indicate the maximum starch/sugar on the label.What are Starches and Sugars in Your Horses Diet?Starch is a blanket word for carbohydrates found in cereal grains such as corn, oats, and barley, said Nichols, but horse owners also need to look at these sugars:Ethanol-soluble carbohydrates (ESC), which are glucose, fructose, and sucrose;Water-soluble carbohydrates (WSC), which are the ESCs plus fructans (chains of fructose molecules); andNonstructural carbohydrates (NSC), which include the starch plus either ESC or WSC.There is no standard for which sugar is listed on a feed tag, said Nichols. This is important to note because if the feed bag is reporting NSC with WSC, it will always be a higher percentage than if the NSC includes ESC only, lacking the fructans.Does a Carbohydrate-Free Diet Exist for Horses?Because carbohydrates in horse feeds can be confusing, some owners try to avoid them altogether. However, horses cannot meet their basic dietary needs without carbohydrates. Horses are herbivores and must consume forage, which is made up of carbohydrates, said Nichols. So, it is important for owners to understand what a carbohydrate is and how much is safe for their horse.Forage or fiber, composed of carbohydrates, should make up the base of a horses diet. Most horses need to consume 2% of their body weight in forage every 24 hours. But owners must understand how much starch and sugar comes into the diet from forage, and the only way to know that comes from testing the hay.Nonstructural Carbohydrates in Horse Feed and ForageNonstructural carbohydrate levels can vary immensely in forages and pastures, which is why Nichols mantra is test, dont guess. Cool-season grasses such as timothy hay can be 10-18% NSC but warm-season grass such as bermudagrass or teff hay can be lower at 6-12% NSC.These numbers are only relevant if you know what your horse needs. For example, for metabolically sensitive horses, the total NSCs in the diet should be 10-12%; 10% NSC if using ESC and 12% if using WSC.But forage doesnt provide all the nutrients horses need, so they must receive a ration balancer or other concentrates, which also contain NSCs. For an average metabolic 1,100-pound horse fed 2% of his body weight in forage, the horse needs 22 pounds of forage and should consume no more than 12% NSC in the total diet. If the hay is 10% NSC, and the horse needs 4 pounds of a supplemental feed for a properly balanced diet, the feed can be as high as 21% NSC while still maintaining a total diet of 12% NSC.Its a lot of math, but the point is the lower your feeding rate, the more wiggle room you have on the NSC level of your concentrated feed, said Nichols. However, you have to know what your hay tests in order to calculate the variables and pinpoint exactly what is acceptable from the feed.Now, I am probably not ever going to recommend a 21% NSC feed for a true metabolic horse, but I would be comfortable feeding one with 15% to 16% NSC in this example because I measured the hay and know it tested at a level that gave me the extra wiggle room in terms of the total diet NSC content, she added.If you are not confident making these calculations, reach out to a qualified equine nutritionist for help.Take-Home MessageAs herbivores, horses depend on fiber in their diets. If a horse must consume a low-starch diet, its important to calculate how much starch and sugar they need in the total diet, which includes supplements and concentrate. This means you have to send your hay for analysis, said Nichols. There is no possible way to curate a starch-controlled diet without this.