Sugars in Spring and Fall Pastures

Pasture forages are an excellent, natural source of feed for horses. Well-managed, high-quality pastures with desirable forage species can meet or exceed the nutritional requirements of many horses.

However, horses with certain metabolic conditions which make them prone to laminitis may need to have grazing restricted to avoid the risk of laminitis or founder. These conditions include Equine Metabolic Syndrome, insulin dysregulation, and sometimes Pituitary Pars Intermedia Dysfunction (PPID; AKA Cushing's disease). For these horses, high intake of non-structural carbohydrates like sugars, starch, and fructans can result in extremely high blood insulin levels, which often triggers laminitis. It is important for owners of these horses to work with a veterinarian to decide whether the horse can graze fresh pasture or if it should only be fed low-NSC hay. Metabolically normal horses can graze pastures safely as long as they do not become overweight.

Non-structural carbohydrates (NSC) are impossible to completely avoid in an equine diet. They are present in pasture, hay, grains, and commercial concentrates. Plants use NSC as an energy source for growth. The NSC are made during photosynthesis when the sun is shining. At night, the plant uses up the NSC from the daytime for growth. This results in a daily fluctuation of NSC levels in plants, meaning that the highest NSC levels are at the end of the daylight hours and the lowest NSC levels are at the end of the night and early morning (see Figure 1).

However, there is an important exception to this rule in the spring and the fall. When nighttime temperatures start to drop, the plant process that uses up NSC slows down. As overnight temperatures dip to 40-45°F, the overnight utilization of NSC decreases dramatically. As a result, NSC levels do not drop overnight and are still high in the morning. A series of bright, sunny days followed by cool nights can cause plants to accumulate very high levels of NSC (see Figure 2).

If you own a horse that is prone to laminitis, be aware of this pattern in the spring and fall when nights are cool!