The sugars in grass are collectively known as Non-Structural Carbohydrates (NSC), which primarily consist of simple sugars like glucose and fructose, as well as starches and long-chain fructans. Fructans are the main energy storage molecule in cool-season grasses and are difficult for some animals to digest in large quantities. Understanding the daily fluctuation of these carbohydrates is important because excessive intake can trigger serious health issues, such as laminitis in horses. Generally, the most concentrated level of NSC occurs in the late afternoon or early evening, which is a direct result of the plant’s natural daily cycle.
The Daily Rhythm of Carbohydrate Production and Storage
The concentration of sugars within grass blades is governed by two opposing biological processes: photosynthesis and respiration. Photosynthesis is the process where a plant uses sunlight, water, and carbon dioxide to create sugars for energy and growth, occurring during daylight hours. As the sun rises and light intensity increases, the rate of sugar production accelerates, manufacturing glucose and converting it into storage molecules like fructans.
This sugar creation continues throughout the day, causing a steady accumulation of NSC inside the plant’s tissues. The plant holds these reserves until it needs them, typically when energy demands are high or light is unavailable. Consequently, the peak level of stored sugar is observed right before dusk, after a full day of sunlight has maximized photosynthetic output.
Once the sun sets, photosynthesis stops, but the plant’s energy consumption, known as respiration, continues. Respiration is the process of using stored carbohydrates to fuel growth, maintenance, and other metabolic activities, which happens 24 hours a day. Throughout the night, the grass uses its accumulated sugar reserves for growth, effectively drawing down the NSC levels.
This overnight consumption results in the lowest concentration of sugars in the grass just before dawn, typically between 3:00 a.m. and 6:00 a.m. The daily cycle is a continuous ebb and flow, where daytime production outpaces nighttime consumption, leading to a high-low swing of carbohydrate content. This understanding allows for a more informed decision regarding grazing times for sensitive animals.
Environmental Conditions That Spike Sugar Levels
While the time of day dictates the rhythm of sugar fluctuation, environmental stressors can increase the total amount of NSC stored, overriding the typical daily pattern. One significant factor is low temperature, particularly a frost or temperatures below 40°F (4°C), especially when followed by bright sunlight. In these conditions, photosynthesis continues to produce sugars, but the cold temperatures inhibit the plant’s ability to use those sugars for growth and respiration overnight.
The sugars become trapped and accumulate in the plant’s cells, leading to high concentrations that can persist for extended periods. This means that grass on a frosty morning or during a cool, sunny fall day can pose a greater risk than grass on a warm summer afternoon. Plants also hoard sugars as a survival mechanism when subjected to other forms of stress.
Drought conditions, where the plant has limited access to water, can trigger a defense response that involves concentrating sugars. Similarly, nutrient deficiencies, particularly low levels of nitrogen, force the plant to convert carbohydrates into storage compounds instead of using them for protein synthesis and tissue growth.
The accumulation of NSC means that stressed, stunted, or overgrazed pastures often contain higher sugar levels than healthy, actively growing forage. High light intensity itself, independent of temperature, also contributes to elevated sugar levels by maximizing the photosynthetic rate. Extended periods of intense, unobstructed sunshine lead to increased sugar production that the plant cannot utilize immediately. These factors can cause the grass to be unsafe for sensitive animals even during the morning hours, which are typically considered the lowest-risk grazing time.
Managing High Sugar Grass for Animal Health
For owners of horses and other grazers sensitive to high sugar intake, managing access to pasture is the primary strategy for mitigating health risks. Adjusting the grazing schedule to align with the lowest NSC concentration is the most direct intervention. This means turning animals out to graze in the early morning, ideally between 3:00 a.m. and 10:00 a.m., and bringing them in before the late afternoon accumulation begins.
Restricting the volume of grass consumed is an effective method, often achieved by using grazing muzzles. These devices reduce the amount of forage an animal can ingest, forcing a slower, regulated intake of carbohydrates without eliminating pasture turnout. Maintaining pasture health is also important, as overgrazing forces the plant to concentrate sugars in the bottom three to four inches of the stem.
Managing the carbohydrate content of supplemental forage like hay is necessary. Soaking hay in water for 30 to 60 minutes can leach out a significant portion of the water-soluble sugars. Before feeding, the water must be discarded to remove the dissolved carbohydrates.
Owners should be aware that certain grass species, such as perennial ryegrass, are genetically predisposed to store higher levels of NSC than others. Utilizing low-sugar forage options or testing the pasture and hay for NSC content provides the most specific data for creating a safe and balanced diet. Implementing these strategies helps ensure that sensitive animals can still benefit from turnout while minimizing the risk of sugar-related health complications.