By means of a nitrogen free diet the time period for the attainment of the endogenous nitrogen level has been established in sheep. It appears that the preliminary protein period is a determining factor in the length of the nitrogen free period. Sheep on a 14 per cent. protein were reduced to endogenous level in 14 to 15 days, while sheep kept on an 8 per cent. protein attain the endogenous level from the sixth to the eighth day of nitrogen-free feeding.
The partition of the urinary end products on a nitrogen free ration is discussed and special consideration is given to the maintenance requirement of sheep. It has been shown in this study, that the maintenance requirement of protein of a 100 lb. sheep is less than advocated in the usual standards.