Determination of digestible and available amino acids in meat meal using conventional and caecectomized cockerels or chick growth assays

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Abstract
1. The present study was designed to compare true digestible amino acid values for meat meal with available amino acid values. True digestible values were determined with a 48 h excreta collection assay using conventional (CONV) and caecectomized (CEC) cockerels. Available values for lysine, methionine and cystine were estimated by chick growth assays.2. True digestibilities of all sixteen measured amino acids (expressed as a proportion of the total) were lower for CEC than for CONV cockerels, with the average difference being approximately 0.10.3. Chick growth assays based on total weight gain indicated that the availabilities of amino acids expressed as a proportion of the total amino acids in meat meal were: 0.70 for lysine, 0.75 for methionine and 0.48 for cystine. Partitioning weight gains to reflect only growth attributable to supplemental crystalline amino acid or meat meal intake consistently yielded higher availability values than when total weight gains were used.4. True digestibility values determined with CEC cockerels were in better agreement with chick available values than were true digestibility values determined with CONV cockerels.5. The amounts of amino acids present in the caeca of meat meal-fed CONV cockerels at 48 h after feeding were small when compared with those levels voided in the excreta and those levels consumed in the feed.6. Multiple regression analyses of excreta and caecal amino acid profiles at 12 and 48 h after feeding suggested that significant amounts of non-digested dietary amino acids flowed into the caeca and were subsequently metabolized by the caecal microflora.