Assessment of lysine bioavailability in an intact protein mixture: comparison of chick growth and precision-fed rooster assays

Abstract

A lysine deficient purified L-amino acid diet was used in a 10-day chick growth assay to estimate the availability of lysine in a corn gluten meal, sesame meal, meat-and-bone meal (CGM-SM-MBM) protein mixture. This mixture had been used previously to construct a lysine-deficient assay diet for growing puppies. The amino acid pattern of the CGM-SM-MBM mixture was also simulated and fed to examine the effect of excess amino acids on lysine availability. Excess amino acids in the CGM-SM-MBM mixture depressed the efficiency of lysine utilization, regardless of whether the excess amino acids were provided as the CGM-SM-MBM mixture or as free L-amino acids. Slope-ratio regression analysis (weight gain regressed on supplemental lysine intake) yielded lysine bioavailability estimates for the protein mixture of 56% (relative to the L-lysine standard curve) but 93% when slope of the CGM-SM-MBM curve was related to slope of the line resulting from feeding L-lysine·HCL + amino acids to simulate those provided by the intact-protein mixture. Partitioning weight gain into that resulting from lysine consumed in the basal diet per se and that resulting from lysine supplements per se provided a more accurate estimate of the efficiency of lysine utilization from each source. This method gave estimated bioavailabilities of 80% for the lysine in CGM-SM-MBM (relative to the L-lysine standard curve), but 93% when related to the slope of the line resulting from regressing partitioned gain on intake of L-lysine consumed in the form of the CGM-SM-MBM simulated amino acid mixture. True digestible lysine in the CGM-SM-MBM mixture was also determined by means of a 48-hour excreta collection assay using force-fed cecectomized or conventional (shamoperated) adult cockerels. Differences among bird-types were not observed. The true digestibility of lysine was estimated to be 90%.