The timing of feeding fresh grass to livestock is a complex practice rooted in plant science and animal physiology. Determining when to feed grass focuses on maximizing the nutritional return for the herbivore, extending beyond simple calendar dates. Proper forage management timing directly impacts the health of the digestive system and the quality of nutrient intake. Understanding the biological state of the plant is the basis for successful grazing and feeding strategies.
Nutritional Maturity Stage
The nutritional content of grass is inversely related to its biological maturity. Young, rapidly growing grass in the vegetative stage offers the highest concentration of digestible nutrients for grazing animals. This stage features lush, leafy growth and high moisture content, resulting in forage with elevated crude protein levels, sometimes exceeding 20% of the dry matter.
As the plant develops, it transitions through the boot stage, where the seed head swells within the leaf sheath, and eventually reaches the reproductive stage. This shift fundamentally changes the plant’s structure and chemical composition. The plant channels energy into forming a seed head instead of creating highly digestible leaves.
Once the grass reaches full maturity, the proportion of structural carbohydrates increases significantly. The plant develops a rigid support structure composed of cellulose, hemicellulose, and the largely indigestible compound known as lignin. This rise in fiber content causes a simultaneous decrease in the overall digestibility and crude protein concentration of the forage. Forage quality is highest in the vegetative state and drops as the plant becomes more fibrous.
Seasonal Readiness for Grazing
The ideal feeding time is heavily influenced by the type of grass and current weather patterns, which affect both availability and safety. Cool-season grasses, such as fescue and orchardgrass, exhibit their greatest productivity and nutritional value during the cooler temperatures of spring and fall. Conversely, warm-season grasses, including sudangrass and sorghum, are best suited for grazing during the peak heat of summer, providing forage when cool-season varieties experience a growth slowdown.
Grazing too early in the spring presents a specific metabolic hazard due to the accumulation of non-structural carbohydrates (NSC), or sugars and starches. High NSC content is most pronounced on days with cool nights and bright, sunny days, conditions that limit the grass’s ability to use the sugars it produces through photosynthesis. This surge in sugar is particularly risky for insulin-sensitive herbivores, such as horses. Excessive NSC intake can overwhelm the hindgut and lead to laminitis, a painful inflammatory condition. Limiting grazing during these high-risk periods, especially in the early morning when sugar levels are often highest, helps mitigate this danger.
A seasonal consideration is the risk of prussic acid poisoning in the fall, which affects warm-season grasses like sudangrass and sorghum. A stress event, such as the first frost, can rupture plant cell walls, allowing compounds within the plant to mix and form toxic hydrocyanic acid. Ruminants are especially susceptible because their digestive process rapidly releases this toxin. Following a killing frost, animals should be withheld from grazing these susceptible plants for approximately five to seven days until the toxin has dissipated. Caution is necessary after a light, non-killing frost, as new regrowth may contain extremely high concentrations of prussic acid.
Safe Introduction and Dietary Transition
The physiological readiness of the herbivore is as important as the biological state of the grass when determining the best time to feed. Any sudden change in forage type, whether from hay to fresh grass or between different types of hay, can lead to digestive upset. The digestive tract of herbivores hosts a diverse population of microbes that require time to adapt to new sources of fiber and nutrients.
A gradual dietary transition is necessary to prevent conditions like colic, bloat, or hindgut acidosis. The microbial community in the gut typically takes 7 to 14 days to adjust to a new forage. Starting with a conservative approach, such as allowing access to fresh pasture for only 15 to 30 minutes on the first day, is a common management practice.
The duration of grazing should be slowly extended over the course of two weeks, with the animal’s behavior and manure consistency closely monitored. Providing hay or other dry forage immediately before turnout helps prevent the animal from gorging on the new grass. This gradual introduction supports the stability of the gut environment and minimizes risks associated with sudden shifts in fiber and moisture content.