New formal approaches to the determination of energy and amino acid requirements of chicks.

Body weight and the intake of metabolizable energy of chicks as function of age, were resolved into a linear equation from which the energy requirements for maintenance and growth were extracted. The metabolizable energy requirement for maintenance was calculated to be 1.91 and 1.62 Cal./g. 2/3, and that for weight gain was 2.05 and 2.19 Cal./g. for male White Rock and female 2--8-week old Leghorn chicks, respectively. The amino acid requirements of growing broiler chicks were calculated from the maintenance requirements, body weight gain and body weight, the proportions of feather protein in total body protein, and the amino acid composition of carcass and feathers. The requirements thus calculated, correlated well with various values in the literature. Diets formulated on the basis of the present model, were lower in protein and amino acid contents than those formulated on the basis of NRC allowances. These differences were pronounced in diets designed for 6--8 week old chicks. The weight gains obtained were similar for both types of diets. Feed conversion were slightly poorer and abdominal fat higher in chicks fed the model diets. It is concluded that the present model can serve, at least as an initial approach, to calculate the protein and amino acid requirements.