IN-SITU DISAPPEARANCE OF AMINO-ACIDS FROM GRASS SILAGES IN THE RUMEN AND INTESTINE OF CATTLE

Nineteen grass silages were evaluated using the in situ rumen and mobi le nylon bag techniques to determine the amino acid (AA) composition o f rumenun-degradable protein and the possibility of predicting the con centrations of individual AA presented to the duodenum from the dietar y AA profiles. All feeds and residues from the nylon bags were analyze d for diaminopimelic acid to correct for contamination by microbial pr oteins. All essential AA. behaved similarly; the initial feed had the highest concentrations, and the material remaining in the mobile nylon bag had the lowest concentrations. The reduction in the concentration of methionine between the 12-h rumen residue and the residue in the m obile nylon bag was significant. With the exception of arginine (r(2) = 0.76) and serine (r(2) = 0.82), the relationship was poor between th e concentrations of AA in the grass silage and those in the residue in the nylon bag following 12 h of rumen incubation. The lack of reliabl e relationships between concentrations of individual AA in the silages and concentrations of AA in the 12-h rumen residue indicated that deg radability characteristics of AA in grass silage were not alike. This poor relationship was likely the reason that prediction equations coul d not be developed between the AA composition of the initial feed and the pattern of AA presented to the duodenum following 12 h of rumen in cubation. The AA composition of the rumen-undegradable portion of gras s silages differs from the AA composition of grass silages.