Body protein and energy accretion in response to dietary protein level in mice from weaning to maturity

The accumulation of body protein and body energy in mice from weaning to maturity as a response to dietary protein level was studied. Seven groups of ddY male mice were fed for 75 d purified diets with a range of 15-70% protein concentration, calculated on a gross energy basis. The food intake and body weight data were analyzed by nonlinear regression to Parks' feeding and growth equation, and data of body protein (%) and body energy (kcal/g) were analyzed using stepwise multiple regression. Body protein (~17%) was independent of both dietary protein level and age. Body energy, as a function of time after weaning, increased to a plateau at about 30 d after weaning. At every dietary protein level the accumulation of body protein and energy increased with age asymptotically to a plateau at ~40 d and ~30 d after weaning, respectively. At every dietary protein level, the protein accretion rose rapidly with age to attain a maximum at about 7 d after weaning, when it depended on the dietary protein level, then decreased markedly to where differences due to dietary protein level became negligible. It is clearly shown in this study that manipulation of dietary protein levels has a greater effect on protein growth and energy gain during the pre-peak part of the body protein accretion and body energy accretion curves than during other portions of those curves.