Methionine substitutes in ruminant nutrition I: Stability of nitrogenous compounds related to methionine during in vitro incubation with rumen microorganisms

Abstract Thirty-one nitrogenous compounds with possible methionine activity were included as potential nitrogen sources in media for in vitro incubation of rumen microorganisms. Compounds not supporting cellulose digestion were included in studies of ammonia release and specific analyses designed to confirm resistance of the compounds to microbial deamination. N -Acetyl- dl -methionine (IV) and dl -homocysteine thiolactone hydrochloride (XIV) were highly stable when added individually and were selected for more intensive study. When added in combination with urea, XIV was more stable than IV as indicated by cellulose digestion, ammonia release data, and specific GLC analysis for the compounds. Compound XIV was also tested in aqueous buffers at pH 6.8 and 2.3. Little destruction was observed within 24 hr at either pH. These results indicate that dietary XIV has good potential for escaping rumen destruction in a form suitable for subsequent conversion to methionine.