Bioavailability of the Digestible Lysine and Total Sulfur Amino Acids in Meat and Bone Meals Varying in Protein Quality

Experiments were conducted to determine whether the digestible Lys, Met, and TSAA in a high and low quality meat and bone meal (MBM) were totally bioavailable for protein synthesis in chicks. True digestibility of amino acids (AA) in the two MBM was determined by the precision-fed cecectomized rooster assay. Bioavailability of the digestible AA was then assessed in three slope-ratio chick growth assays using Lys-, Met-, or TSAA-deficient crystalline AA basal diets that were supplemented with varying levels of the test AA, high or low quality MBM, or AA mixtures simulating the mean digestible AA composition of the high and low quality MBM. Response parameters were weight gain, feed efficiency, body N gain, and body Lys gain in the Lys assay and weight gain and feed efficiency in the Met and TSAA assays. Bioavailability values for the digestible Lys, Met, and TSAA in the MBM and AA mixtures simulating MBM varied depending on response parameter, with values based on feed efficiency generally being highest. No consistent differences in bioavailability of the digestible AA were observed between the two MBM when all AA were considered; however, the bioavailability of the digestible Lys in the low quality MBM was lower than that in the high quality MBM for two of four performance criteria. When considering all response parameters and the AA mixture results, bioavailability of the digestible Lys and Met in the two MBM was generally 90% or greater, whereas bioavailability of the digestible TSAA was only 80% or less. The results of this study indicated that essentially all of the digestible Lys and Met in MBM were bioavailable for protein synthesis and metabolism but suggested that a significant amount of the TSAA, particularly Cys, was not bioavailable.