Effect of low protein diets with amino acid supplementation on broiler growth

Reduction of litter N and ammonia production can be accomplished by decreasing dietary CP to levels below the requirements listed by the National Research Council. However, amino acids must be added to low CP diets to obtain satisfactory growth performance. It is important to know what levels of amino acid supplementation are required in low CP diets to avoid decreased growth performance and feeding excess amounts of expensive ingredients. Two studies were conducted to determine if further supplementation with essential amino acids (EAA) or nonessential amino acids (NEAA) or energy to corn-soybean meal diets low in CP (17.3 or 17.7% CP and already supplemented with multiple essential amino acids) could improve growth of broilers during Weeks 2 and 3. Ten cages of six males were assigned to each of eight treatments per study. In both trials, a high CP diet (22.6 or 23.0%) resulted in higher BW gain and gain to feed ratio (GFR), compared with all other treatments. In Experiment 1, adding Arg, Thr or Trp, but not Ile nor Glu, increased BW gain and feed intake. Supplemental Thr improved GFR. In Experiment 2, supplemental Thr + Trp + Arg was beneficial in the presence of extra energy or NEAA. The results of Experiment 1, but not of Experiment 2, suggest that the low CP diet was not limiting in NEAA but had insufficient Thr.