Protein Metabolism in the Rumen. I. Absorption of Glycine and Other Amino Acids

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Abstract
The absorption of glycine, serine, threonine, methionine sulfoxide, aspartic acid, asparagine + glutamine, isoleucine, and leucine from the rumen was demonstrated both in vitro and in vivo. Four amino acids not normally present in human blood were found in ruminant blood. These chromatographed on Dowex 50-X8 like phosphoserine and cysteic acid, phosphethanolamine, and methionine sulfoxide. Eleven different acidic and neutral amino acids were found in rumen fluid from a steer fed normal rations of grain and hay. Serine was present in highest concentration. Methionine sulfoxide appeared in the rumen fluid after methionine was added to the rumen. The data show that amino acids can be absorbed from the rumen and thus contribute to the absorption of N from the alimentary tract.