Ever been confused by the recommendation of keeping the non-structural carbohydrates (NSC) under 10-12% for metabolic issues with a horse? It can be overwhelming to try to find the right type of feed to fit the criteria. However, the 10% does not really tell the whole story about NSC content in the feed. This is because it is a percentage, not an absolute amount. To really know how much NSC is in a feed you need to know the amount of feed you are going to feed as well as the percentage of NSC in the feed.
A feed that has a low feeding rate, even though it has a slightly higher NSC, can be perfectly adequate for a metabolically challenged horse. Keep in mind that NSC is the sum of starch and sugar in a feed.
Let’s take for example the Modesto Milling Horse Supplement Pellet. The NSC content is 14%, which is considered low starch, but not as low as the 10% recommended. Although this may be slightly above the recommended level for horses with metabolic issues, since it has a very low feeding rate (1 lb/day) it would not be a problem, especially if you split the 1 lb recommended feeding into 2 meals of 1/2 lb each. You see, in 1 lb of Modesto Supplement Pellet with 14% NSC there is only 2.2 oz starch (16 oz x 0.14 = 2.2 oz). If you feed ½ lb of the Modesto Supplement Pellet 2x day that will be only 1.1 oz starch per feeding (8 oz x 0.14 = 1.1), which is a very small amount if you consider the overall size of the horse and the total amount of food a horse is consuming (probably more than 20 lbs).
The 10% NSC recommendation comes from the amount of starch that will not cause a significant glycemic response in the horse.
Physiologically, 1.1 oz of starch fed to a 1,100 lb horse would hardly result in any more of a glycemic response than the hay would. To put this into perspective, the levels of starch in a meal found in research that will result in a moderate rise in blood glucose are >1 g starch per kilogram body weight or > 100g starch/100 kg BW. To convert to pounds, that would be 3.5 oz starch per 220 lbs body weight or 17.5 oz starch per 1100 lb horse. Clearly, 1.1 oz of NSC in a ½ lb of Modesto Milling Supplement Pellet is well below the 17.5 oz of starch threshold defined in research and for this reason we can be confident that it will not result in a glycemic response over what meal of hay would.