Pasture grass serves as the foundation of grazing systems, representing a diverse and dynamic plant community that sustains livestock across the globe. This forage is instrumental to the agricultural industry, providing the primary, cost-effective feed source for ruminants like cattle, sheep, and goats. Beyond its role in animal husbandry, pasture land is an important part of ecological balance, influencing soil health, water cycles, and biodiversity. Understanding the composition and management of these grazing lands is central to efficient food production and environmental stewardship.
Defining Pasture Grass
Pasture is defined as land covered with perennial vegetation, typically a mix of grasses, legumes, and other herbaceous plants, that is actively grazed by livestock. It differs from hay, which is forage that has been cut, dried, and preserved for later consumption, primarily by its high moisture content. Fresh pasture grass typically holds around 70% to 80% water, while hay is dried to contain less than 20% moisture.
Pasture is also distinct from turf grass, such as a residential lawn, which is selected for aesthetic qualities and tolerance to frequent, close mowing. Pasture plants, in contrast, are chosen for their palatability, high yield, and ability to withstand repeated grazing and hoof traffic. A defining characteristic of good pasture is its persistence, meaning the ability of the plants to regrow quickly and robustly after being defoliated by grazing animals.
Major Types and Varieties
The plant species that constitute pasture are generally categorized by their optimal growing temperature, leading to two main groups: cool-season and warm-season grasses. Cool-season grasses, known as C3 plants, thrive in temperatures between 60 and 75 degrees Fahrenheit, making them productive in the spring and fall. Common examples of cool-season varieties include Tall Fescue, Orchardgrass, and Ryegrass.
Warm-season grasses, or C4 plants, utilize a different photosynthetic pathway that allows them to flourish in hotter conditions, generally from 80 to 95 degrees Fahrenheit. These grasses, which include Bermuda, Switchgrass, and Big Bluestem, provide forage during the summer months when cool-season varieties often go dormant. A diverse pasture environment also includes non-grass species like legumes, such as clover, and forbs (broad-leafed non-woody plants). Legumes are valuable because they fix atmospheric nitrogen into the soil, improving soil fertility and increasing the overall nutritional quality of the forage.
Nutritional Value for Livestock
Pasture grass is the primary source of nutrients for grazing livestock, and its quality is assessed by key metrics like crude protein (CP), energy content, and fiber fractions. Crude protein, necessary for growth and milk production, can range widely, depending on the species and maturity. Young, rapidly growing grass in the vegetative stage has a higher protein and energy content than mature grass.
Energy content is measured as Total Digestible Nutrients (TDN), which indicates the total energy available to the animal. Fiber content is determined by Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) values. These values influence how much forage an animal can consume and how digestible it is. NDF measures the total fiber that affects feed intake, while ADF measures the less digestible fiber components like cellulose and lignin that impact digestibility. For instance, a lactating cow requires forage with fiber not higher than 50% NDF and 34% ADF for optimal productivity.
As the grass matures and enters the reproductive stage, the concentration of fiber (NDF and ADF) increases, while the levels of CP and TDN decline, reducing overall nutritional quality. Legumes tend to maintain a higher nutritive value and have a less rapid decline in digestibility as they mature compared to grasses. Therefore, managing the timing of grazing to keep plants in a younger, vegetative state maximizes the nutritional return for the livestock.
Managing Sustainable Pastures
Sustainable pasture management focuses on mimicking natural grazing patterns to improve the health and productivity of the entire ecosystem. Rotational grazing involves frequently moving livestock between small sections of pasture, called paddocks, giving previously grazed areas a period of rest and regrowth. This technique prevents continuous grazing, which can lead to overgrazing, depletion of soil nutrients, and a reduction in plant growth.
During the rest period, pasture plants replenish their root reserves, stimulating deeper root growth and enhancing the overall health of the stand. Stronger, deeper root systems improve soil structure, increase the soil’s capacity to absorb and retain water, and mitigate soil erosion. Manure and urine are also distributed more evenly across the pasture, returning essential nutrients to the soil and fostering microbial activity.
Well-managed pastures offer environmental benefits by protecting natural resources like soil and water. Healthy soil rich in organic matter can capture and store atmospheric carbon, which is an aspect of carbon sequestration. By promoting plant diversity and preventing soil degradation, rotational grazing ensures that the pasture remains productive and resilient against challenges like drought and extreme weather.