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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Dietary Forage Source and Crude Protein Level on in Vitro Microbial Protein Synthesis and Ruminal Fermentation

item Olmos Colmenero, J - UW MADISON
item Broderick, Glen

Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2004
Publication Date: July 26, 2004
Citation: Olmos Colmenero, J.J., Broderick, G.A. 2004. Effect of dietary forage source and crude protein level on in vitro microbial protein synthesis and ruminal fermentation. [abstract]. Journal of Dairy Science. 87(1):217.

Technical Abstract: Optimizing microbial protein synthesis in the rumen is crucial because it represents more than half of the nonammonia nitrogen that reaches the duodenum in dairy cows. A 3x5 factorial arrangement of 15 diets, three forage sources [alfalfa silage (AS); 50% alfalfa silage:50% corn silage (AS:CS); corn silage (CS)] at each of 5 CP levels (13.5, 15.0, 16.5, 18.0, and 19.5% of DM) were tested in two identical ruminal in vitro incubations. Diets contained (% of DM) 50% forage and 50% concentrate. High moisture corn was replaced with solvent soybean meal to increase CP. The marker used for microbial NAN synthesis (MNS) was 15N. After 4 and 8 h of incubation, samples were taken to obtain total solid pellets, supernatants, and isolated bacterial pellets. Supernatants were analyzed for NH3, total AA, and VFA. Total solid and bacterial pellets were analyzed for DM, total N and 15N to estimate true dry matter digestibility (TDMD) and net MNS (blank corrected). Concentration of total AA, acetate, and total VFA were higher for AS and AS:CS compared with CS. However, propionate concentration and TDMD were higher on AS:CS than on AS and CS. Net MNS was higher on CS than on AS and AS:CS. Levels of dietary CP affected only NH3 and total AA concentrations. As expected, NH3 and total AA increased with dietary CP content. Under the conditions of this study CS was more effective for stimulating net microbial NAN production than AS and AS:CS; CP level had no effect on net MNS.

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