Degradation of Amino Acids by the Mixed Rumen Microbial Population

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Abstract
Degradation of physiological quantities of amino acids by rumen microbes was determined under both in vitro and in vivo conditions. In vitro rate constants for EAA indicated that Arg and Thr were rapidly degraded (.5 to .9 mM/hr); Lys, Phe, Leu and Ile formed an intermediate group (.2 to .3 mM/hr); and Val and Met were least rapidly degraded (.1 to .14 mM/hr). In vivo EAA degradation rates were about 1.5× greater than estimates derived from in vitro rate constants, but a significant (P<.05) linear relationship between in vitro and in vivo rates suggested that similar degradative pathways predominated in both systems. Incubating Thr, Arg, Lys, Phe, Leu and Ile alone or in combination with a mixture of EAA yielded similar amounts of degradation for these EAA. Met and Val degradation was approximately twice as great (P<.05) when fermented alone vs in conjunction with other EAA. Combining a mixture of NEAA (Asp, Ser, Glu, Ala, Tyr, Orn) with the EAA mixture did not influence EAA degradation. Tyr and Orn were the only NEAA degraded to lesser (P<.05) extents (30%) when the fermentation system contained both NEAA and EAA mixtures. Data presented demonstrated that specific amino acids are degraded at different rates and that there are interactions between certain amino acids. With the possible exception of Met, supplements of free amino acids cannot survive ruminal degradation. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science