Bioavailable amino acids in corn and alfalfa as measured by applying the true metabolizable energy assay

Amino acid (AA) availabilities were determined in three different samples of corn and one of dehydrated alfalfa using the true metabolizable cnergy (TME) assay and force-feeding the ingredients both singly and mixed with a basal diet. One of the corn samples and the alfalfa were those used in the ANRC collabortative study on metabolizable energy (Sibbald, 1978). The other two corn samples were the same cultivar but one (corn D) was afflicted with the fungal disease, "eye spot" (kabatiella zeae), and had a lower hectoliter weight than the nondiseased counterpart (corn ND). Values were calculated for both the apparent AA availability (AAAA) and true AA variability (TAAA), i.e., corrected for the metabolic and endogenous AA losses. Some of the AAAA values for corn ND and corn D varied appreciably with the method of feeding, but such variations were not reflected in the TAAA values. However, the AAAA and TAAA values of alfalfa were generally similar when fed alone or mixed with the basal diet. For the ANRC corn sample both the parameters varied substantially with generally higher AAAA and TAAA values being obtained by feeding the corn mixed with the basal diet. The AA availability values of corn D were very similar to those of its counterpart corn ND as well as the ANRC corn. Discussed are the implications of measuring AA availability in feedstuffs applying the TME assay and using the ingredients as such or as a complete diet.