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Combinations of Nitrogen Sources for Starch Digestion by Mixed Rumen Bacteria^{1, 2,}

Department of Animal Sciences, University of Kentucky, Lexington

ABSTRACT

The effectiveness of all two-way combinations of arginine, aspartic acid, glutamic acid, lysine, methionine, proline, serine, and valine as nitrogen sources for in vitro starch digestion by mixed rumen bacteria has been compared with that of urea and individual amino acids. Three-way and four-way combinations of aspartic acid, glutamic acid, lysine, proline, serine, urea, and valine were also evaluated. Thirteen of the 28 pairs tested significantly increased starch digestion, but only aspartic acid and lysine, aspartic acid and valine, and valine and serine approached the effectiveness of urea. The responses to these pairs exceeded simple additive effects. All three-way and four-way combinations tested significantly (P<.01) increased digestion in at least one trial. The most effective combination tested was urea, valine, aspartic acid, and lysine. Increased starch digestion appeared to be closely associated with ammonia concentrations after four and eight hours.

¹ The investigation reported in this paper (no. 67-5-102) is in connction with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.

² This investigation was supported in part by contract no. AHd2-39(c) with the Beef Cattle Research Branch, Animal Husbandry Research Division, Agricultural Research Service, USDA.