NSC for All Seasons: Carbohydrate Levels in Horse Pastures

Grass is a natural food for horses, and many equines get along well with unrestricted pasture access at any time of the year. For certain horses with health problems like metabolic syndrome or insulin resistance, free-choice consumption of grass can lead to bouts of laminitis, an intensely painful and sometimes fatal inflammation of the structures within the hoof. For these horses that are highly sensitive to the nonstructural carbohydrates (NSC, including starches and sugars) in grass, grazing must be avoided or at least restricted to times when foliage energy level is at a very low level.

Most horse owners know that NSC can be abundant when grass is actively growing during the spring, summer, and early fall months. However, considering the sugar that’s stored in plant foliage and the spikes in photosynthesis that can occur on sunny days during late fall and early spring, even grass that looks dormant may not be safe for some horses to graze. Having grass samples tested is the only way to determine the NSC level in pasture foliage.

In the U.S., some regions never get cold enough to trigger dormancy. Other parts of the country experience below-freezing temperatures for months at a time, guaranteeing that no plant growth is taking place. Much of the country lies somewhere between these extremes, experiencing a recurring pattern of colder and then milder weather periods. While a few hours of sunshine in February won’t get the grass growing, a week of significantly warmer days in mid-winter could lead to NSC production in states with borderline climates.

Theoretically, horse owners could test grass samples every month to keep track of NSC levels, keeping in mind that sampling the same pasture in the early morning and late afternoon could result in different numbers. Probably the safest way to manage horses that are sensitive to pasture carbohydrate levels is to keep these equines in a drylot most of the time, feeding a low-carbohydrate hay free-choice and allowing pasture access only when the horses are wearing closed muzzles that do not give access to any fresh grass.