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Grass Quantity VS Quality

May 12, 2020

by Caleb Weiss, Cow/Calf Product Manager

Forage quantity and quality often drive the need to provide supplemental feeds to meet a grazing animal’s requirements for energy, crude protein, minerals, and vitamins. Recent years have shown that even if grass is abundant, cows can still struggle to maintain body condition. The inconsistencies in forage characteristics create challenges for producers who want to maximize herd productivity.

Quantity

The grazing season refers to the time of year in which animals are grazing actively growing forages and generally occurs in spring, summer, and early fall (FGTC, 1992). During the spring, young forages can be sparse and may not contain enough dry matter to fulfill the animal’s nutrient requirements. Stocking cattle on pasture too densely or too early may result in over-harvesting, which can reduce the plant’s ability for regrowth and negatively impact forage quantity and quality for the remaining season. Grazing livestock at the maximum carrying capacity of the pasture increases the risk of forage quantity shortfalls if the lack of rain or other circumstance prevents normal growth. Additionally, overgrazing is associated with exposing more ground surface to the sun which will increase soil moisture losses. As the season progresses and forage density increases, not enough grazing pressure can lead to shading of the plants by overlapping plant material. It can decrease the ability for photosynthesis and reduce the plant’s nutritive value, resulting in over mature wasted forage (Van Soest, 1994).

Quality

When plants make up the main dietary component, forage quality is determined by animal performance. Interaction between intake potential, digestibility, and the utilization of nutrients within the animal will drive how well a grazing animal will perform. Energy deficiencies can occur early in the season, as there may be good quality grass, but not enough of it for the animals to consume to meet their needs (Ball et al., 2001). Energy is one of the most important nutrients to consider in spring because it coincides with the greatest requirement of the cow during the late stages of pregnancy and early lactation (NRC, 2000). As the growing season progresses and forage dry matter content increases, the nutritive value of the forage begins to decline. This also holds true with abundant late season growth if an area receives higher than normal precipitation. The reduction in forage quality is generally associated with the proportion of lignified structural tissue in the plant, which increases as it gets older. Temperature, light, and water can alter the maturation process of plants, and can be highly variable throughout the year (Van Soest, 1994). When forage quality decreases, the amount of forage that needs to be consumed to meet the animal’s requirements increases. This can be a problem because passage of the consumed forage through the digestive tract slows down when forage quality is low. Slower digestion results in increased gut-fill, or the physical capacity of the rumen, and may limit the amount that the animal can consume. Energy is often the limiting factor for grazing livestock; however, there are incidences where protein or minerals are the nutrients that can reduce animal performance. At weaning, forage may not contain adequate protein or mineral levels to meet a calf’s requirements for proper bone and muscle development and will result in poorer performance (Ball et al., 2001).

In general, forage quantity increases while forage quality decreases throughout the growing season. Supplementation strategies are often based on visual estimates of forage quality and quantity; however, the feed energy per unit of area is not necessarily consistent with forage yield and can result in costly mistakes (Davis et al., 2002). For more information on grazing cattle supplementation, please contact your local QLF representative.

Citations

Ball, D.M., M. Collins, G.D. Lacefield, N.P. Martin, D.A. Mertens, K.E. Olson, D.H. Putnam, D.J. Undersander, and M.W. Wolf. 2001. Understanding Forage Quality. American Farm Bureau Federation Publication 1-01, Park Ridge, IL.

Davis, G.V., M.S. Gadberry, and T.R. Troxel. 2002. Composition and nutrient deficiencies of Arkansas forages for beef cattle. Prof. Anim. Sci. 18:127-134.

Forage and Grazing Terminology Committee. 1992. Terminology for grazing lands and grazing animals. J. Prod. Ag. 5:191-201.

NRC. 2000. Nutrient Requirements of Beef Cattle. (8th Ed.). The National Academic Press, Washington DC.

Van Soest, P.J. 1994. Nutritional Ecology of the Ruminant. (2nd Ed.). Cornell University Press, Ithaca, NY.

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