Effects of levels of dietary protein and digestible energy on growth, feed utilization and body composition of growing mice

Abstract

Three experiments were designed to determine the responses of growing mice, when fed diets adequate in indispensable amino acids, minerals, vitamins and fatty acids to different levels of dietary digestible energy (DE) and protein. In experiment 1, three DE levels (15.48, 17.15 and 18.83 MJ kg −1) and three crude protein (CP; N×6.25):DE ratios (7.31, 8.13 and 8.94 g MJ −1) were tested in a factorial experiment. Increasing dietary De above 15.48 MJ kg −1 did not improve growth or DE intake and had no effect on body fat or protein gain. An optimum CP:DE ratio exceeding 8.94 was indicated. In experiment 2, seven CP:DE ratios were compared (8.13, 8.50, 8.94, 9.38 9.75, 10.19 and 10.56) and 9.2 was found to be adequate. In experiment 3, a diet containing 15.95 MJ DE kg −1 was reduced in DE by additions of 10, 20, 30, 40 and 50% cellulose. Feed intakes increased until diets contained about 25% cellulose (about 12 MJ DE kg −1) but mice were unable to obtain their DE requirements when diets fell below about 13.6 MJ DE kg −1, when cellulose was the fibre component in a purified diet.