I am a veterinarian, and I have treated a client’s draft-cross horse for laminitis. This gelding is somewhat insulin resistant and was overweight at the time of initial assessment. First, the horse receives a balancer pellet with 6.6% starch and 4.2% sugar, so the total NSC (nonstructural carbohydrate) content is 10.8%. What does “sugar” mean? Does it mean the ESC (ethanol-soluble carbohydrate) or WSC (water-soluble carbohydrate) content? Second, are values such as those listed above a guaranteed maximum generally? How consistent are they from batch to batch? Third, 6.6% is a higher amount of starch than we typically see in grass hays In Nevada and California. I'm not sure there are any studies showing how that would affect insulin levels. Typically, I worry more about the WSC than anything but I just don't see starch levels much above 2 or 3% in grass hay. Grain hays may be different, but I tell my clients that own insulin resistant horses to not feed grain hays.
Just so we’re on the same page, NSC = WSC + starch. The value that you were given for the particular feed, a balancer pellet, is WSC, not ESC, and it should be consistent from batch to batch because that product is a “fixed' formula and the amounts of each of the ingredients do not change. Granted, some of the ingredients may vary a little in NSC from one year to another, but nothing that contributes to the NSC is included in high amounts, which is why the balancer pellet is considered a low-NSC feed.
I think that the values you are concerned about have to be given perspective. We are talking about a percentage, in this case 10.8% NSC, not an absolute value. The feeding rate of the feed in your scenario is 1 to 2 lb per day. If the horse is fed 1 lb a day and only 10% is NSC, then the horse is only getting one-tenth of a pound of NSC (starch/sugar) total from the feed. That is very little starch and sugar. When such a small amount of something is fed, whether the product is 10% or 20% NSC or whether the measurement is ESC or WSC or starch is of little concern because it is all relative to the amount fed. Conversely, if a specific hay has 10% NSC and it is fed at 20 lb per day, the horse consumes 2 lb of sugar/starch a day from the hay.
The type of stored nonstructural carbohydrate in hays varies depending on the type of plant. Cool-season perennials (orchardgrass, timothy, fescue, etc.) store carbohydrates in the form of sugars (almost no starch). Warm-season perennials (Bermuda, tifton, etc.) and alfalfa store their carbohydrates as starch and sugar. Grain hays also store their carbohydrates as starch and sugar. Grain hays can be rather high in NSC, up to 20%, so these should not be fed in very large amounts to a horse with insulin resistance. The warm-season and cool-season perennials are much lower in NSC and, depending on the harvest, are better choices for these horses. Alfalfa can be low in starch/sugar but too high in calories for an overweight horse.
Rate of intake is another factor that plays a role in the way the body processes nonstructural carbohydrates. Because both starch and sugar are absorbed as glucose once digested, the slower something is eaten the slower it goes into the bloodstream and the lower the insulin response. Feeding smaller meals is another way to combat glucose and insulin spikes in the bloodstream because the glucose peaks are relative to the amount fed. So, any management system that can slow intake will help horses, as will feeding smaller, more frequent meals.
Kentucky Equine Research has a product for balancing a hay/pasture-only diet that is suited to insulin resistant horses. Called I.R. Pellet, this pelleted, palatable supplement has a lower feeding rate than the balancer pellet, typically 2 to 4 oz per day. The major difference in a ration balancer and I.R. Pellet is the amount of protein each contributes to the diet. I.R. Pellet is only a vitamin and mineral supplement; it does not supply a significant amount of protein. Most balancer pellets are formulated to supply protein, vitamins, and minerals. I.R. Pellet is another option for a seriously overweight horse.