Response surface analyses of the effects of dietary protein on feeding and growth patterns in mice from weaning to maturity

Responses of food intake, protein intake, gross energy intake and body weight of mice from weaning to maturity of dietary protein level were studied. Thirteen groups of ddY male mice were fed purified diets covering the entire range (0-100%) of protein concentration on a gross energy basis for 68 d. The food intake and body weight data in each group were analyzed by nonlinear regression to obtain values of the six parameters in Parks' feeding and growth equations. These parameters, found as a function of the protein content of diet, were then used to construct the response surfaces of food intake and body weight over the dietary protein versus age space. At every protein level the daily energy intake rose rapidly with age to a plateau at about 7-14 d after weaning and was maintained throughout the experiment. Daily energy intake was independent of the dietary protein content except at very low dietary protein contents. Consequently, from 21 to 89 d of age daily protein intake was directly proportional to dietary protein level. These results imply that mice ate for energy rather than protein when fed diets varying in protein content in the range of 10-80%. Body weight as a function of time after weaning increased to a plateau at every dietary protein level, but the details of the pattern of growth were affected by the dietary protein level. Further, the response surface of body weight versus dietary protein level and age was analyzed to find the protein requirement of mice for maximal growth during a given interval from weaning.