Ruminal NH3-N and BUN concentrations were altered by YMFC (T2) supplement which containing high cassava-based diets As NH3-N is regarded as the most important nitrogen source for microbial protein synthesis in the rumen in addition, the result obtained was closer to optimal ruminal NH3-N(15-30%mg, Wanapat and Pimpa,1999; Chanjula et al., 2003,2004) for increasing microbial protein synthesis feed digestibility and voluntary feed intake in ruminant fed on low-quality roughages