Grass is the fresh, growing forage, consumed immediately by grazing animals. Hay is the same grass that has been harvested and cured to remove moisture, allowing for long-term storage as feed. The fundamental difference lies in the dramatic reduction of water content and the resulting changes in nutritional profile and physical application.
Grass: The Living Plant
Grass is a living organism characterized by a very high moisture content, typically ranging between 70 and 80% of its total weight. This high water level makes it an excellent source of hydration for grazing animals. The nutrient profile of fresh grass is rich in easily digestible proteins, starches, and sugars.
The high moisture and nutrient density mean that fresh grass is metabolically active, continuing to respire and consume its own sugars even after being cut. This characteristic makes it entirely unsuitable for storage; cut grass left in a pile would quickly ferment, mold, and spoil due to microbial activity. Therefore, grass serves as a feed source for immediate consumption through grazing or cutting for fresh feeding.
Hay: The Transformation and Curing Process
Transforming grass into hay involves a managed process designed to halt biological degradation and achieve preservation. This process begins with mowing the grass, often using specialized equipment that may condition or crimp the stems to accelerate drying. The goal is to rapidly reduce the moisture content to a level that inhibits the growth of spoilage organisms like mold and bacteria.
The critical phase is curing, where the cut forage is spread out in a thin layer, or swath, and exposed to the sun and wind. Raking or tedding the material turns it over, ensuring uniform drying and preventing the bottom layers from retaining moisture. This field-drying process targets a final moisture content of approximately 15 to 20% for safe baling and storage.
Reaching this low moisture level is necessary to prevent aerobic respiration and microbial heating, which can otherwise lead to spoilage or even spontaneous combustion in densely packed bales. Common forage species like Timothy, Bermuda, and Alfalfa are frequently used for hay production because they cure well and retain acceptable nutrient levels. The resulting cured product is a stable, dense feed that can be stored for months or years, serving as the main diet source when fresh pasture is unavailable.
Key Differences in Nutritional Value and Application
The curing process fundamentally alters the nutritional composition, creating distinct differences between the two feed types. Fresh grass, with its high water content, is generally more digestible and higher in certain unstable vitamins, such as Vitamin E and Vitamin A precursors. It also contains higher levels of beneficial Omega-3 fatty acids, which are largely lost during the drying and storage required to make hay.
Hay is a more concentrated source of dry matter. While some nutrients are lost during curing—specifically, a decrease in protein and digestible energy due to plant respiration and leaf shatter—the remaining fiber content is relatively high. This makes hay a more physically demanding feed for animals to digest, promoting gut motility and serving as an excellent source of necessary roughage.
The difference in application is primarily driven by storability and energy concentration. Grass is the preferred feed for immediate grazing, offering a complete, natural diet during growing seasons. Hay is an indispensable commodity for winter feeding, drought conditions, or for animals that are housed and do not have access to pasture. The low moisture content of hay allows it to be safely transported and stored, making it a reliable, year-round forage base.