Dietary Effects of Soy Isoflavones on Growth and Carcass Traits Of Commercial Broilers

Three experiments (EXP) were conducted to determine the effect of soy isoflavones (ISF) on growth and carcass traits of commercial broilers. The EXP were conducted simultaneously and a common control was used. In each EXP, treatments were replicated five times with five chicks each. Average initial and final BW were 102 and 2,890 g, 102 and 2,657 g, and 102 and 2,803 g for EXP 1,2, and 3, respectively, and the EXP were conducted from 9 to 52 d posthatching. In EXP 1, the effects of graded levels of supplemental ISF above those typically found in a corn-soybean meal (C-SBM) diet were studied. The treatments were 1) C-SBM, 2) C-SBM + ISF levels two times those in C-SBM (2×), and 3) C-SBM + ISF levels five times those in C-SBM (5×). The 2× and 5× levels of ISF decreased gain:feed (linear, P \u3c 0.04) but increased (P \u3c 0.04) breast weight compared with the C-SBM diet. Other performance and carcass traits were not affected (P \u3e 0.05) by treatment. In EXP 2, the effects of low ISF levels in a C-soy protein concentrate (C-SPC) diet were studied. The treatments were 1) C-SBM, 2) C-SPC (low ISF), and 3) C-SPC + ISF (ISF levels equal to those in C-SBM). Average daily gain (ADG) and average daily feed intake (ADFI) were decreased (16 and 9%, respectively; P \u3c 0.01) in chicks fed the C-SPC diets, regardless of ISF level. Gain:feed of chicks fed the C-SPC + ISF diet was decreased 9% (P \u3c 0.02) compared with chicks fed the C-SBM diet, and gain:feed of chicks fed C-SPC was intermediate between the two. Carcass traits were not affected (P \u3e 0.05) by treatment. In EXP 3, the effects of low ISF levels in a low CP diet were studied. The treatments were 1) C-SBM, 2) low CP (17,14, and 12% in the starter, growing, and finishing diets, respectively) with supplemental crystalline amino acids (low CP-AA), and 3) low CP-AA + ISF (ISF levels equal to C-SBM). Daily gain and gain:feed were decreased from 7 to 9% (P \u3c 0.01) in chicks fed the low CP-AA and low CP-AA + ISF diet relative to those fed the C-SBM diet. Abdominal fat pad percentage was increased (P \u3c 0.01) in chicks fed the low CP-AA diets compared with those fed the C-SBM diet. Dietary ISF can affect ADG and ADFI and may affect carcass traits in some instances

Glycine Supplementation to Low Protein, Amino Acid-Supplemented Diets Supports Optimal Performance of Broiler Chicks

Six experiments were conducted to determine the effects of low CP in diets for broilers and to evaluate limiting essential and nonessential amino acids (AA) in these diets. All experiments were conducted with Ross x Ross broilers in brooder batteries from 0 to 17 or 18 d posthatch. Treatments were replicated with 6 pens of either 5 or 6 broilers each. In Experiment (Exp.) 1, corn-soybean meal diets were formulated to 16.18, 17.68, 19.18, 20.68, or 22.18% CP. The 22.18% CP diet provided 1.23% Lys and 0.89% TSAA, met or exceeded all nutrient requirements of young broilers, and served as the positive control (PC) diet in all experiments. Increasing dietary CP linearly increased final BW, daily gain (ADG), and gain:feed (G:F) (P \u3c 0.005). In Exp. 2, additions of crystalline essential (EAA) or nonessential AA (NEAA) were added to the low CP diet to simulate the AA profile of the PC. Daily gain, final BW, and G:F were decreased (P \u3c 0.01) when CP was reduced, but the addition of the NEAA increased final BW, ADG, and G:F (P \u3c 0.07) to the level of broilers fed the PC. Addition of EAA alone was without effect. In Exp. 3, chicks fed diets with supplemental Glu, Ala, Asp, or Pro had reduced daily feed intake (ADFI), ADG, and final BW (P \u3c 0.05) compared with the PC diet. Addition of Gly or the combination of Gly, Glu, Asp, Ala, and Pro to the low CP diet increased G:F (P \u3c 0.01) compared with chicks fed PC, and ADG was not different from that of broilers fed the PC diet. In Exp. 4, chicks were fed either the PC diet, the low CP diet with Gly + Ser concentrations of 1.23, 1.35, 1.47, 1.59, 1.71, 1.83, 1.95, or 2.07%, or a 10th diet that contained 1.23% Gly + Ser and with Glu to equal the N concentration of the 2.07% Gly + Ser diet. Final BW, ADG, and G:F were increased linearly (P \u3c 0.001) as the concentration of dietary Gly + Ser was increased. Chicks fed the low CP diet with 2.07% Gly + Ser had growth performance that was not different from that of chicks fed the PC. The addition of Glu to the low CP diet was without effect. In Exp. 5, chicks were fed the PC with additions of 0, 0.15, or 0.30% Gly or the low CP diet containing 1.60, 1.72, 1.84, 1.96, 2.08, 2.20, or 2.32% Gly + Ser. Glycine addition to the PC had no effect, but Gly addition to the low CP diet increased G:F linearly (P \u3c 0.001). Growth performance of chicks fed the low CP diet with 2.32% Gly + Ser was equal to that of chicks fed the PC diet. In Exp. 6, chicks were fed the PC or the low CP diet containing 1.80, 1.95, 2.10, 2.25, 2.40, 2.55, 2.70, 2.85, or 3.00% Gly + Ser. Glycine addition to the low CP diet increased G:F linearly (P \u3c 0.001). In summary, low CP diets result in optimal growth of broilers with Gly + Ser levels of 2.44%. ©2006 Poultry Science Association, Inc