Articles on forages, animals, and grazing systems
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Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Good grazing management will result in improved pasture yields. Understanding how plants grow allows for better management decisions as to when to move livestock under different growing conditions. This article will focus on growth occurring after grazing or mowing. All plants require water, nutrients, and energy to grow. The current season, climate, and other environmental factors also affect plant growth. Extensive defoliation caused by grazing too closely, lack of a sufficient rest period, and environmental stress caused by drought, high temperatures, or flooding can severely reduce the productivity of a forage stand.
Energy, which is produced through photosynthesis in the green leaf area, is required for growth. Carbohydrates, the energy stores for the plant, are first used to maintain the plant. After these needs are met, plant growth occurs. Any excess carbohydrates are stored within the plant until needed for growth in the spring or after defoliation and for support of respiration during winter dormancy.
Grasses regrow using the remaining leaf area and by utilizing stored carbohydrates. It is critical that adequate leaf area remains after grazing to minimize depletion of stored energy. Thus, the recommendation that fescue and orchardgrass plants be grazed to a 3-4 inch height and then allowed a rest period. Tiller management is also critical for a healthy grass stand. Basal buds in the crown develop into new tillers when the growing point of the initial tiller is removed. The shoots or tillers produce new leaves and stems. If grazing or mowing is managed correctly to stimulate tiller growth, stand yield may increase and the grass will start to regrow more rapidly.
Legumes are more dependent on stored carbohydrates for regrowth. Legumes stems are composed of the growing point, stem, leaves, nodes, and axillary buds in comparison to the tillers in grasses. Legume stems begin to grow in length and leaves are arranged on opposite sides of the stem. In the spring, stems grow from dormant crown buds using stored carbohydrates. All leguminous species have tap roots in comparison to grasses which have fibrous root systems. The tap root systems are ideal for carbohydrate storage. Legumes mainly depend on the carbohydrates stored in the roots for regrowth. Because legumes are not as dependent on remaining leaf area for regrowth, leaving high leaf area is not necessary.
In all species, it is essential to maintain healthy root systems in order to produce healthy plants. The root system not only stores carbohydrates, but allows for the uptake of water and nutrients for plant functions, and anchors the plant to the ground as well. Close grazing or continuous grazing depletes the stored carbohydrates that are needed for both top growth and root growth. Depleted root systems make plants less drought tolerant. Allowing plants to have an adequate rest period and not overgrazing pastures keeps root systems healthy and productive.
Pastures should be managed to favor the desired forages. It would be easiest to manage one species as various plant species should be managed differently. Because of the many advantages, species from the various groups, especially grasses and legumes, are often mixed in pastures. Grasses and legumes differ in the way they regrow and need to be grazed accordingly.
Certain forages such as Kentucky bluegrass, Bermudagrass, white clover, and other low growing species have a growing point that remains low throughout the growing season and can tolerate closer grazing. Tall growing forages, such as tall fescue, smooth brome, orchardgrass, switchgrass, alfalfa, and red clover, elevate the growing point as they mature and need to be managed more carefully. In pastures containing both grasses and legumes, it is usually suggested to manage to favor legume growth. Grazing or mowing to low heights favors plants that depend more on root reserves as it takes off a large amount of leaf area. Therefore, grazing to lower heights will favor legumes.
Using a rotational grazing or management intensive grazing method increases pasture production and quality as well as animal performance. Continuous grazing depletes carbohydrate reserves which reduces future productivity. Plants need to be given an adequate rest period to regrow and accumulate storage reserves. Because legumes rely mainly on stored energy for regrowth, frequent defoliations are especially harmful. It is suggested that legumes are given 30-35 days between defoliations. Continuously grazing tall grasses suppresses new growth. Most of the leaves are grazed off along with the basal tillers which greatly decreases production and can deplete stored energy. Moving the livestock quickly is best. It is important that individual plants are not grazed twice during the same rotation. The length of the rest and grazing periods and the stocking density will be dependent on the available forage, season, and other environmental factors. There are many different species of forages that are commonly used in Kentucky. Each species is unique and should be managed accordingly in order to optimize plant and animal production. Understanding the traits of the forages on your farm can be useful to make the best management decisions to maximize forage yield, forage quality, and herd health and production.