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Title: Grass vs. legume forages for dairy cattle

item Jung, Hans Joachim

Submitted to: Nutrition Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2008
Publication Date: 9/16/2008
Citation: Paulson, J., Jung, H.G., Raeth-Knight, M., Linn, J. 2008. Grass vs. Legume Forages for Dairy Cattle. Proceedings of the 69th Minnesota Nutrition Conference, September 16-17, 2008, Owatonna, Minnesota. p. 119-133.

Interpretive Summary:

Technical Abstract: Alfalfa is the primary forage fed to lactating dairy cows; however, there is renewed interest in utilizing grass forages in lactating dairy cow diets particularly because of farm nutrient management issues. Yield and perceived quality is generally lower for grass species compared to legumes while other agronomic factors such as longer stand life, requirement for nitrogen fertilizer, and more tolerance of manure spreading, which allows for greater and more frequent manure application than on alfalfa, may make grasses more desirable. Grasses may also complement diets with high levels of co-products from the ethanol and food industries better than legumes because grasses are generally moderate to low in crude protein (CP) compared to alfalfa and most co-products contain a significant amount of CP. The purpose of this paper is to review some results and limitations of previous lactation studies that have compared the feeding value of grass and legume forages and to provide information on nutritional and cell wall differences between grasses and legumes in order to better understand the utilization of these forages by dairy cows. Given the complexity of factors that determine the composition and digestibility of forages, blanket statements claiming superiority of alfalfa or any other forage for milk production are impossible. High levels of performance have been observed for cows fed either legume or grass forages when included as part of a typical total mixed diet with multiple ingredients. The standard advice to feed high quality (low fiber, high digestibility) forages to lactating dairy cows as part of appropriately balanced mixed diets still prevails. However, the criteria or parameters on which to formulate diets to optimize milk production from grasses is less well understood than it is for alfalfa or corn silages. Current forage analysis methods are incomplete in identifying the chemical or nutritional components in grasses which alter their digestion and support high milk production. Better methods of forage evaluation are needed to discriminate among and between forage species as to their nutritional superiority and quality. Although in vitro or in situ NDF digestibility analysis can offer some information about forage quality, these tests alone cannot account for all the relevant sources of variation that determine forage quality.