Determining the sugar content in grass is a crucial step for owners managing the diets of grazing horses, particularly those susceptible to metabolic conditions like laminitis or Equine Metabolic Syndrome. Testing grass for sugar, specifically Non-Structural Carbohydrates (NSC), allows horse owners to make informed decisions about pasture access and overall feed management. Accurate measurement of NSC is the only way to determine if pasture forage is safe for sensitive animals, since visual appearance alone is not a reliable indicator of sugar levels.
Defining Non-Structural Carbohydrates (NSC)
Non-Structural Carbohydrates represent the energy reserves stored within the plant cells, distinct from the structural carbohydrates that form the plant’s cell walls, such as fiber and cellulose. NSC includes simple sugars (like glucose and sucrose), starch, and a storage carbohydrate called fructan. High levels of these compounds can cause a spike in blood glucose and insulin, which is linked to an increased risk of laminitis in metabolically sensitive animals.
The concentration of NSC in grass is highly variable, changing based on environmental factors. Photosynthesis, driven by sunlight, creates sugars during the day, causing NSC levels to peak in the late afternoon or evening. Conversely, plants consume stored carbohydrates at night for growth, leading to the lowest NSC concentrations around sunrise.
Other factors also influence the grass’s sugar content, including temperature and moisture. When growth is slowed by cold temperatures, drought, or lack of nitrogen, the plant may accumulate sugars because it is producing more than it is using for growth. For example, a cold, sunny morning promotes sugar production but the cold temperature inhibits the plant’s ability to use or store that energy for growth, resulting in high sugar levels.
Proper Techniques for Grass Sampling
Obtaining an accurate sample is the foundation of a successful test. The sampling process should mimic the horse’s grazing pattern, taking clippings from multiple random areas across the pasture to create a single, composite sample. Use sharp scissors or clippers to cut the grass at the height the horse typically grazes, often close to the ground, as NSC is primarily stored in the lower stem base.
The combined clippings should be mixed thoroughly and reduced to a representative subsample of about a half-pound. The metabolism of carbohydrates in the fresh grass must be halted immediately to prevent the sugar content from changing before testing. The most reliable method is to place the sample into an airtight bag, squeeze out the air, and promptly freeze it, which stops the enzymatic breakdown of the sugars.
When shipping the sample to a laboratory, it must be kept frozen to maintain integrity, often requiring overnight shipping with frozen ice packs. Shipping wet or unfrozen samples can lead to inaccurate results due to continued metabolic activity during transit. Choosing a certified laboratory experienced in equine forage analysis is also important for accurate processing and reporting.
Methods for Analyzing Sugar Content
The gold standard for determining grass NSC levels is professional laboratory analysis, which provides a comprehensive breakdown of carbohydrates. Laboratories typically use wet chemistry methods to measure Water Soluble Carbohydrates (WSC), Ethanol Soluble Carbohydrates (ESC), and starch. Total NSC is calculated by adding the WSC and starch components together.
The results are reported as a percentage on a dry matter (DM) basis, meaning the water content has been removed from the calculation. This standardized percentage is used for comparing the grass’s safety against established guidelines. Fructans, included in the WSC fraction, are not digested in the small intestine and ferment in the hindgut, posing a significant laminitis risk.
Some owners consider using a refractometer, a handheld device that measures Brix, as a simple at-home testing method. While refractometers measure simple sugars, they do not measure starch or fructans, which are a major component of NSC in cool-season grasses. Relying on a refractometer reading alone is insufficient and can be misleading for managing horses at risk of laminitis, making laboratory testing the only dependable option.
Actionable Management Based on Sugar Levels
Once the laboratory analysis is complete, the resulting NSC percentage provides the basis for managing pasture access. For horses with a history of laminitis, insulin resistance, or Equine Metabolic Syndrome, a total NSC level (WSC + Starch) of less than 10% on a dry matter basis is recommended. Some veterinarians advise aiming for levels as low as 8% for highly sensitive animals.
If the tested grass exceeds the safe threshold, management strategies must limit the horse’s intake of high-sugar forage. Since NSC levels are lowest in the early morning, restricting grazing to the period between late night and mid-morning significantly reduces sugar consumption. Using a grazing muzzle is also effective, as it can reduce grass intake by up to 80% while allowing the horse to remain on pasture.
When grass NSC levels are consistently high, it may be necessary to remove the horse from the pasture entirely and feed a tested low-NSC hay in a dry lot. Regularly monitoring the pasture during high-risk times, like spring, fall, or after a cold snap, allows owners to make timely adjustments to grazing schedules and reduce metabolic risk.