Limiting amino acids after methionine and lysine with growing turkeys fed low-protein diets

The effectiveness of Thr and other amino acids (AA) replacing CP in Met- an d Lys-adequate diets of Large White male turkeys was studied from 6 wk to m arket age. Experiment (EXP) 1 examined efficacy of Thr and an AA grouping i n corn-soybean (CS) diets containing 82.8 and 77.0% of NRC CP and in corn-s oybean-canola-meat (CSCM) diets containing 85.2 and 79.4% of NRC (1984) CP. Experiment 2 compared AA responses in CSCM diets containing 100, 92.5, 85, and 77.5% of NRC (1994) CP. Compared with control CP, 1) 92.5% of NRC CP s upported maximum BW, and supplemental Thr or Trp was without effect; 2) 82. 8 to 85.2% of NRC CP resulted in reduced BW and breast meat yield (BMY), an d supplemental Thr or Trp was ineffective in reversing this reduction, and 3) 77 to 79% of NRC CP resulted in depressed BW and BMY. Supplemental Thr p rovided a substantial positive BW but no BMY response, whereas a combinatio n of Thr, Ile, Val, Arg, and Trp completely returned BW and partially retur ned BMY to that of the normal CP control. Turkeys on CS and CSCM assay diet series supported BW responses to CP and AA similarly. We concluded that in low-CP diets containing Met and Lys to requirement, supplemental Thr resul ted in improved BW, whereas Thr, Ile, Val, Trp, and Arg returned BW, but no t BMY, to normal CP control.