Studies on quantitative and qualitative effects of lucerne silages with varying nitrogen fractions on ruminal nitrogen metabolism and the ruminal bacterial population

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In ruminant nutrition lucerne silage is a forage with considerable ecological and nutritional potential. However, already prior to ensiling are extensive metabolic reactions in the plant material occur, which may be considerably affected by wilting conditions and may have a significant influence on crude protein composition and, thus, protein quality of the silage produced. In the case of grass silages differing wilting conditions lead to silages with a high percentage of true protein on the one hand whereas, the degradation of crude protein during wilting continues to advance in other silages and leads to high percentages of non-protein N. We assume that there are similar processes in lucerne silage and that they influence the quality of the silages considerably. Because of the mutual dependence of ruminal N and carbohydrate metabolism it can be hypothesized that the differing composition of N fractions leads to extensive alterations in ruminal metabolism. The basis of the submitted project is production of lucerne silages with differently composed N fractions due to different wilting conditions. After an extensive chemical characterization of these silages, their effects on ruminal N as well as carbohydrate metabolism will be studied by means of a semi-continuous long-time rumen simulation system. Because of the differing substrate supply it can be assumed that shifts will be observed in the ruminal microbial population and there will be specific samples taken to track these changes by molecular genetic methods. Especially silage varieties with high percentages of free amino acids might facilitate growth of amino acid-fermenting species leading to an increase of N turnover accompanied by less efficient rumen microbial crude protein synthesis. The results of this project will significantly contribute to the knowledge of silage making. Already during wilting the later quality of lucerne silages could be purposefully influenced. With that lucerne silages that ensure efficient microbial crude protein synthesis in the rumen might be produced.