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Six experiments (EXP) were conducted to evaluate growth performance of different breed crosses of broiler chicks fed diets containing soybean meal, soy protein isolate (SPI), soy protein concentrate (SPC), or rice and casein. Cornish x Plymouth Rock (CxPR; EXP 1, 3, 4, 5, and 6) or New Hampshire x Columbian (NHxC; EXP 2 and 4) cross chicks were used. The chicks were fed a corn-soybean meal (C-SBM) diet before allotment to treatment. The age of the chicks ranged from 5 to 9 d posthatching at the start of the EXP, and the assay periods ranged from 8 to 14 d. Initial weights were 194.9, 96.1, 102.1, 84.7 [84.1 (CxPR) or 85.3 (NHxC)], 101.8, and 145.1 g in EXP 1 to 6, respectively. A completely randomized design was used in all EXP, and treatments were replicated four to six times with four or five chicks each. All diets were formulated to meet the NRC nutrient requirements of chicks. In EXP 1 (CxPR male chicks) and EXP 2 (NHxC female chicks), gain and gain:feed (G:F) were greater (P < 0.01) in chicks fed the C-SBM diet compared with chicks fed diets containing SPI. In EXP 3, CxPR chicks were fed a C-SBM diet, a SPI-dextrose-cornstarch diet (dextrose:cornstarch, 1:1) formulated by Louisiana State University Agricultural Center (LSU) or a similar SPI diet (dextrose:cornstarch, 0.53:1) formulated by the University of Illinois (UI). Daily gain, average daily feed intake (ADFI), and G:F were increased (P < 0.01) in chicks fed the C-SBM diet relative to chicks fed the two SPI diets, and there were only minor differences between the two SPI diets. In EXP 4, the CxPR and NHxC male chicks were fed the same diets used in EXP 3. Daily gain and ADFI were greater in the CxPR and NHxC chicks fed the C-SBM diet relative to chicks fed the SPI diets (P < 0.01), but the increased average daily gain (ADG) and ADFI in chicks fed the C-SBM diet were much greater in the CxPR chicks (chick x C-SBM vs. SPI, P < 0.01). Daily gain, ADFI, and G:F were greater (P < 0.01) in CxPR chicks than in NHxC chicks. In EXP 5, ADG, ADFI, and G:F were greater (P < 0.04) in chicks fed the C-SBM diet compared with those fed a C-SPC diet. In EXP 6, CxPR chicks fed the C-SBM diet grew faster (P < 0.09) than those fed a rice and casein diet. Variable effects of diet on growth of chicks were affected by breed crosses of chicks.

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Poultry Science

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