Role of gastrointestinal microflora in nitrogen and mineral balances in young mice fed on autoclaved and irradiated diets.

Male germ-free (GF) and conventional (CV) mice were fed on steam-sterilized (autoclaved for 30 min at 121 degrees C) and gamma irradiation-sterilized (5 Mrad with 60Co) diets for a one-week adjustment period from 4 weeks of age. During the subsequent week, the amounts of feed eaten were determined, and the feces and urine were collected eaily. The effects of the mode of diet sterilization and intestinal microflora on the feed consumption, body weight gain, feed efficiency (body weight gain/feed consumption), feed N efficiency (body weight gain/feed N consumption), and the excretion, absorption and retention of N, Ca, Mg and P and the bone deposits of these minerals were investigated. 1) The method of sterilization of the diet did not appreciably influence these parameters, except for the apparent digestibility of N and ratio of N retention. Compared to autoclaved diet-fed mice, irradiated diet-fed mice showed a higher apparent digestibility of of N and lower ratio of N retention. 2) Feed consumption in both GF and CV mice showed no major differences. Body weight gain, feed efficiency and feed N efficiency were higher in GF mice than in CV mice. 3) GF conditions increased the apparent digestibility of N, Ca, Mg and P. Lower total excretion of N, Ca and P in the feces and urine, a higher retention of Ca and P, and higher ratios of retention of N and these minerals were observed in GF mice. 4) The results in GF mice indicated a higher weight of moisture- and fat-free bone and a higher Ca, Mg and P concentration in the bones (femurs and tibias with fibulas) with respect to the body weight minus the weight of the digesta.