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

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Abstract
1. The influence of the gut microflora on protein utilization has been investigated with a series of good- and 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 diet containing unheated or heat-damaged albumen (100 g/kg), casein (80 g/kg) and gelatin (100 g/kg); sesame protein (220 g/kg); sesame protein (220 g/kg) supplemented with lysine (5 g/kg); freeze-dried cod muscle (160 g/kg); heat-damaged cod muscle (160 g/kg); mildly-steamed egg albumen (100g/kg); heat-damaged egg albumen (100 g/kg).3. No significant differences in NPU values for the proteins measured in GF 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 be higher in CV chicks than in GF chicks with all proteins except sesame protein, with which uric acid excretion was a little higher in GF chicks.6. Endogenous nitrogen excretion was higher in GF 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.