Growth and development of broiler breeders. 2. Independent effects of dietary formulation versus body weight on skeletal and muscle growth.

The relationship between body weight gain, nutrient intake, and skeletal and muscle growth in broiler breeder pullets was studied in two experiments. A total of 720 and 540 pullets were started in Experiments 1 and 2, respectively. In the first study, growing pullets were fed either a 15% protein, 2,885 kcal ME/kg pullet grower diet or a 23% protein, 3,133 kcal ME/kg broiler starter diet from 2 to 16 wk of age. Within each dietary treatment, there were three body weight groupings (light, control, heavy) achieved by manipulating weekly feed allowances. At 8, 12, and 16 wk of age, 12 pullets from each diet and body weight grouping were killed for muscle [pectoralis major] and skeletal (shank, keel, tibia, clavicle) measurements. As body weight increased, so did skeletal growth, but there were no significant differences in skeletal measurements related to diet. At 12 and 16 wk of age, pullets fed the broiler starter diet had significantly larger p. major muscles. In Experiment 2, growing pullets were fed restricted diets: 1) the 15% protein grower diet (control), 2) the broiler starter diet adjusted weekly to the same calculated calorie intake as that obtained with the grower diet (broiler starter calorie), or 3) the broiler starter diet adjusted to the same calculated protein intake as the grower ration (broiler starter protein). At 16 wk, there were no significant differences between body weight or skeletal measurements of the control and broiler starter calorie treatments. Pullets in the broiler starter calorie treatment did have significantly larger pectoralis muscles and less abdominal fat than those fed the 15% grower diet. Pullets in the broiler starter protein treatment were significantly lighter and had shorter bones, less abdominal fat, and smaller p. major muscles than those in the control treatment.