Effect of low-protein diets on growth performance and body composition of broiler chicks

Three experiments were conducted to investigate effects of dietary manipulations to improve growth performance and whole-body composition of broiler chicks fed low-protein diets supplemented with crystalline amino acids. In all experiments, male chicks (1 d old) were fed a common corn-soybean meal diet (23% CP) for 7 d and subsequently allotted to treatment diets in a completely randomized design (10 chicks per floor pen, six replications). Chicks had free access to the isoenergetic diets (3,200 kcal MEn/kg) for 2 wk, after which chicks were weighed and then fasted for 24 h, and the whole-body DM, N, and ether extract contents of two chicks per pen (and six baseline chicks) were determined. In Experiment 1, Gln or Asn replaced 1% triammonium citrate in the low-protein diet (19% CP). In Experiments 2 and 3, dietary concentrations of crystalline essential and nonessential amino acids, respectively, were increased incrementally in the low-protein diets (19 to 20% CP). In all experiments, chicks fed low-protein diets grew slower, used feed less efficiently, and retained less N and more ether extract than chicks fed the control diets (P less than or equal to 0.05), despite additions of crystalline Gln or Asn and despite increased dietary concentrations of crystalline essential and nonessential amino acids. Chicks fed low-protein diets excreted less N (P < 0.001) than did chicks fed the high-protein diets, and N excretion increased linearly (P < 0.001) with N intake. In summary, low-protein diets failed to support equal growth performance to that of high-protein control diets.