Order of amino acid limitation in poultry by-product meal.

1. Two chick assays (from 8 to 17 d posthatching) were conducted to determine the order of amino acid (AA) limitation in poultry by-product meal (PBPM) using AA deletion and addition assays. 2. In the deletion assay, the basal diet contained 155 g/kg crude protein (provided solely by PBPM) and was fortified with cystine, tryptophan, threonine, lysine, valine, isoleucine, histidine, methionine and phenylalanine to meet the Illinois ideal AA Pattern. Each AA was then deleted individually from the basal diet and its effect on growth assessed. 3. In the addition assay, various individual or combined additions of nine AAs were made to an unfortified 155 g/kg crude protein diet containing PBPM as the sole source of dietary crude protein. 4. The results from the deletion assay were in general agreement with those from the addition assay. Based on the combined results of the deletion and addition assays, the order of AA limitation in PBPM was 1) cystine, 2) tryptophan, 3) threonine and lysine, 5) valine, and 6) isoleucine and histidine with the degree of deficiency of valine, isoleucine and histidine being similar. The results also suggested that methionine may be slightly limiting in PBPM protein.