The utilization of protein and excretion of uric acid in germ-free and conventional chicks.

I. The influence of the gut microflora on protein utilization has been investigated with a series of goodand poor-quality protein diets in germ-free (GF) and conventional (CV) chicks by the measurement of net protein utilization (NPU) and uric acid excretion. 2. The diets used were: 280 g protein per kg dict containing unheated or hcat-damaged albumen (roo gjkg), casein (80 g/kg) and gelatin (100 gjkg); sesame protein (220 g/kg); sesame protein (220 g/kg) supplemented with lysine (5 g/kg); freeze-dried cod muscle (160 g/lcg); heat-damaged cod muscle (160 g/kg); mildly-steamed egg albumen ( roo g/kg); heat-damaged egg albumen (100 g/kg). 3. No significant differences in NPU values for the proteins measured in G F and CV chicks were found, with the exception of unsupplemented sesame protein, for which the NPU value was slightly higher in GF chicks. 4. The replacement of unheated egg albumen by heat-damaged egg albumen in the 280 g protein/kg diet resulted in a decrease in uric acid excretion. With the cod-muscle diets, heat-damaging the protein caused an increase in uric acid excretion. Supplementing the sesame protein with lysine resulted in a decrease in uric acid excretion. 5. Excretion of uric acid tended to bc highcr in CV chicks than in G F chicks with all proteins except sesame protein, with which uric acid excretion was a little higher in G F chicks. 6. Endogenous nitrogcn cxcretion was highcr in G F than in CV chicks. 7. It is concluded that the gut microflora has little influence on the utilization of dietary protein by chicks, although it may modify the route of excretion of the N which survives digestion and reaches the lower gut.