Growth Performance of Different Breed Crosses of Chicks Fed Diets with Different Protein and Energy Sources1,2

ABSTRACT 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 × Plymouth Rock (C×PR; EXP 1, 3, 4, 5, and 6) or New Hampshire × Columbian (NH×C; 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 (C×PR) or 85.3 (NH×C)], 101.8, and 145.1 g in EXP 1 to 6, respectively. A completely randomized design was used in all EXP, and treatments were repli-cated four to six times with four or five chicks each. All diets were formulated to meet the NRC nutrient require-ments of chicks. In EXP 1 (C×PR male chicks) and EXP 2 (NH×C 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, C×PR chicks were fed a C-SBM diet, a SPI-dextrose-cornstarch (Key words: chick, protein source, breed cross