Maintenance requirements for dietary protein in 11- and 18-month-old male rats

Body weight, lean body mass (total weight less body fat), carcass protein, and serum protein were examined as potential parameters by which to assess the effect of age on protein requirements for maintenance in male rats, aged 11 months and 18 months, fed diets containing 1.53, 3.41, 4.98, 6.52, or 8.05% dietary protein, casein plus methionine, for a 5-week period. Body weight change was maintained in older animals at 6.52% dietary protein and in younger animals at 4.98% dietary protein. Older animals consuming the two diets highest in protein had a greater percent body fat and less percent body protein than younger animals. Significant effects of diet and the interaction of diet and age on serum protein were also observed. As dietary protein level increased, serum protein increased gradually in younger rats, but only between 3.41 and 4.98% dietary protein in older rats. Lean body mass and total carcass protein increased as dietary protein level increased, but there were no significant differences due to age or the interaction of diet and age. Changes in body weight indicate a greater protein requirement for 18-month-old rats compared with 11-month-old rats, although complicated by greater food intake and fat deposits in older animals. Measures of body protein indicate that age has some influence on protein needs for maintenance purposes.