Amino Acid Profiles of Total and Soluble Protein in Feedstuffs Commonly Fed to Ruminants

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Abstract
Samples of 19 feedstuffs commonly fed to ruminants were hydrolyzed and profiles of total amino acids determined. The soluble protein fraction was extract- ed in a modified version of Burroughs mineral buffer, hydrolyzed, and analyzed for amino acids. The amino acid content of the insoluble protein fraction was found by difference. In the majority of the feedstuffs analyzed, there were marked differences between the amino acid profile of the total protein and the amino acid profile of the insoluble pro- tein fraction. This suggests that the amino acid profile of the undegraded protein which bypasses the rumen may be differ- ent from the amino acid profile of the dietary protein as originally ingested. If these differences exist in vivo, they will be of consequence in the application of several recently proposed systems for the estimation of metabolizable amino acids which assume no differences in amino acid profile between total and unde- graded feed protein.
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