A: Simple sugars, such as the sucrose found in peppermints and sugar cubes, are absorbed by the horse’s small intestine as glucose and fructose. Glucose causes release of insulin to facilitate the entry of glucose in to cells. Fructose (not to be confused with fructans) is metabolized differently. Only metabolized in the liver, fructose is more lipogenic than glucose, meaning that it’s more likely to lead to production of fat.
Most concern about sugar and starch intake has stemmed from our increasing knowledge about insulin resistance (IR), laminitis, polysaccharide storage myopathies (PSSM), and equine gastric ulcer syndrome (EGUS). Horses with IR release more insulin than is normal in order to remove glucose from their blood stream. As a result, while circulating glucose tends to be normal, circulating insulin is elevated. High circulating insulin creates an increased risk for developing laminitis. Horses with PSSM store glycogen (the storage form of glucose) abnormally in their muscle tissue, and diets high in starch and sugar cause increased production of volatile fatty acids in the gastric stomach causing a more acidic environment and a greater likelihood of a horse developing EGUS
I think it’s important to put the questions of sugar in treats in perspective of a horse’s typical daily non-structural carbohydrate consumption. If we assume a 1,200-pound horse eating 2% of body weight as dry matter from hay a day, and that the hay contains 10% moisture and 10 % nonstructural carbohydrate (NSC) on a dry-matter basis (a value often used as the recommended upper NSC level for horses with metabolic issues, such as IR and PSSM), this horse is consuming 1,090 grams of NSC (starch and simple sugars) per day.
A pure sugar cube weighing about 4 grams is 100% sucrose. The popular round, red-and-white peppermint candies have a human serving size of three pieces (about 15 grams) and of that between 8 and 10 grams are sugar. Traditional peppermint candy canes are heavier at 18 grams and provide about 12 to 14 grams of sugar. You can see that in the context of the above horse’s daily diet these are tiny intakes of sugar. However, there are some important considerations.
When feeding a horse hay, you’re also feeding it proteins and minerals that help buffer stomach acid. Additionally, hay’s fiber component impacts the rate at which the NSC reaches the small intestine and is absorbed. The sugar in sugar cubes dissolves quickly and will move with the liquid fraction of the digesta, which moves more rapidly than larger fibrous particles. This means that that the sugar will likely be absorbed relatively soon after it is fed. This makes it potentially more likely to cause a spike in blood glucose than the NSC contained within hay.
Feeding a healthy horse three or four sugar cubes is unlikely to cause a significant glucose spike; however, for a horse with uncontrolled IR, PSSM, or a laminitis history, feeding sugar cubes isn’t a risk worth taking. Skip the sugary treats, too, if your horse is overweight, especially if he has a cresty neck. After all, every calorie counts and calories from treats mean feeding fewer calories from “real” food. Human research shows that tissues in insulin resistant people are more sensitive to insulin after exercise. This may or may not be the case in horses, but if it is, then your horse might be better able to handle the sugar in these treats when they are given shortly after work.
For the otherwise healthy horse, consuming a candy cane or a few peppermint candies is unlikely to have any major impact.