Influence of gastrointestinal microflora on digestibility and biological value of protein in rats

The influence of the gastrointestinal microflora on the digestibility and biological value of casein was investigated in germ-free (GF) and conventionalized (Cvd) Fischer 344/Yit rats fed an 8% casein diet. There was no significant difference in the true digestibility of casein between GF and Cvd rats, but the apparent digestibility was higher in Cvd than in GF rats. The biological value of casein was significantly higher in GF than in Cvd rats. In the casein diet period, body weight gain was almost the same in GF and Cvd rats, but food intake was significantly greater in Cvd than in GF rats. The excretion of fecal N was similar in GF and in Cvd rats whereas more urinary N was excreted in Cvd than in GF rats. In the protein-free diet period, metabolic fecal N per 100 g of food intake was significantly higher in GF than in Cvd rats, but there was no difference in the excretion of endogenous urinary N per 100 grams of body weight between the GF and Cvd rats. The results indicate that the presence of a gastrointestinal microflora does not influence the true digestibility, but increases the apparent digestibility and decreases the biological value of casein at an 8% level in the diet.