Abstract: It was the aim of this study to characterize the factors which could enhance urea recycling into the rumen and consequently improve N utilization and reduce the N release into the environment. The sources for animal nitrogen are dietary nitrogen and endogenous nitrogen (mainly urea nitrogen). Utilization of dietary nitrogen can be improved by nutritional approaches such as dietary energy-nitrogen synchronization and increasing the portion of Un-degradable Dietary Protein (UDP). This study focused on trials which could improve endogenous N-utilization through manipulation of urea recycling. The study was conducted on isolated rumen epithelial tissue of sheep using conventional Ussing-chamber technique. Feeding conditions prevailing a ruminal pH of 6.0-6.4 seems to be optimal for better urea N utilization and reduction of nitrogen release into the environment. Feeding conditions leading to lower ruminal pH values (<6) can be expected to reduce the use of endogenous urea-N for the synthesis of microbial protein and hence to increase urea excretion via urine with an adverse environmental impact.