In recent years we have seen growing concern about the energy sources used in the horse's diet, in particular starch.
Starch is a long carbohydrate (polysaccharide) stored in plants as an energy reserve. Starch reserves in plants vary, with cereals such as oats, wheat, barley and maize, commonly used in horse feed, having particularly high amounts.
In a horse's diet, starch plays a caloric role, similar to that of fat and fiber. Simplifying a little, in a horse's diet there are two types of carbohydrates: structural (HCE) and non-structural (HCNE).
Structural Carbohydrates (HCE)
Some structural carbohydrates such as hemicellulose and cellulose, structural constituents of plants, play a fundamental role in the horse's diet, meeting its fibrous needs. Most of the HCE in the horse's diet is provided by forage (hay). The digestion of these HCE into volatile fatty acids begins in the cecum, with the help of a microbial flora resident there.
Non-structural carbohydrates (NSHC)
HCNE (starch and sugars) must undergo pre-cecal digestion and absorption (in the small intestine). During this digestive process, starch must be broken down into simpler molecules, identical to sugar, which are easily absorbed. The glucose in circulation can be used immediately by the cells (a process mediated by the hormone insulin), it can be mobilized for fat synthesis or it can be stored in the form of glycogen (in the muscles and liver).
The metabolism of HCNE is particularly important in sports horses when they are subjected to anaerobic activity, since in the absence of oxygen, energy production depends on the use of these glycogen reserves. Insufficient glycogen reserves will result in early fatigue and will limit the horse's performance.