EFFECTS OF DIETARY-PROTEIN LEVEL ON GROWTH AND BODY-COMPOSITION IN MICE DIVERGENTLY SELECTED FOR FAT-CONTENT

A study was conducted to examine the effects of dietary protein percen tage and selection for divergence in fat content on growth and body co mposition in mice. The three lines used had been selected as follows: high epididymal fat pad weight as a percentage of body weight (HF), lo w epididymal fat pad weight as a percentage of body weight (LF) and a randomly selected control (RC). Mice from each line were allotted at w eaning (3 wk of age) to one of four dietary protein percentages: 12, 1 6, 20, and 24%. Growth and efficiency of feed conversion were measured at 2-wk intervals and mice were killed and body composition was measu red at 9-wk of age. Overall, HF mice grew faster, were more efficient at converting feed to body weight gain, and had empty carcasses with a higher percentage of fat (P < 0.05) and a lower percentage of protein than LF mice. However, fat-free empty-body protein and ash percentage s, protein gain, protein gain:protein intake, and protein gain:energy intake ratios were not different among genotypes. As dietary protein p ercentage increased, gain:feed ratio increased quadratically (P < 0.05 ) in all genotypes and was maximized in mice consuming 16% protein. Pr otein gain was maximized in mice consuming 16% protein. Feeding diets providing protein percentages above or below 16% depressed protein gai n and protein gain:energy intake ratio. Genetic line-by-dietary-protei n-level interactions were generally not significant for growth, feed e fficiency and body composition traits.