Limiting order of amino acids in corn and soybean meal for growth of the chick.

Several experiments were conducted with crossbred chicks during the period 8 to 22 d posthatching to establish the limiting order of amino acids (AA) in corn and dehulled soybean meal (SBM) and in a corn-SBM mixture. Cecectomized adult cockerels were used to determine true AA digestibilities in both corn and SBM, and AA fortification levels were based upon bringing digestible AA levels to their ideal levels (expressed as a percentage of CP). Ideal ratios (percentage of lysine) used were Lys, 100; sulfur AA (SAA), 72; Arg, 105; Val, 77; Thr, 67; Trp, 16; Ile, 67; His, 37; Phe+Tyr, 105; and Leu, 111. Diets were fed at 10% CP, but they contained corn or SBM in amounts that would just meet the ideal concentration of the AA in greatest excess (Leu for corn; Phe for SBM). Thus, the corn diets contained only 5.6% CP from corn whereas the SBM diets contained only 8.0% CP from SBM. Diets were adjusted to 10% CP from AA additions, with glutamate varying as necessary. The limiting order of AA in corn was 1) Lys, 2) Thr, 3) Trp, 4) Arg, Ile, and Val, 5) Met+cystine, 6) Phe+Tyr, and 7) His. In SBM, the limiting order was 1)Met+cystine, 2) Thr, 3) Lys and Val, 4) nonspecific amino nitrogen, and 5) His. The order of limiting AA in the corn-SBM mixture was 1) Met, 2) Thr, 3) Lys, 4) Val, 5) Arg, and 6) Trp.