The efficiency of dietary N by dairy cows is generally low, and in part, may be related to an impaired utilization of N in the rumen. A major determinant of microbial protein synthesis is the availability of energy-yielding substrates (Castillo et al., 2001). It seems likely that low ratios of effective rumen degradable protein (ERDP) to fermentable metabolisable energy (FME) will restrict microbial protein synthesis and dry matter intake and, consequently, lead to reduced milk yield (Cabrita et al., 2003). Nitrogen excretion in faeces and urine accounts for a high proportion of N intake, which may be more than 70% of the daily N consumption. Environmental pollution from N as ammonia and nitrates is regarded as a major potential problem world wide. Nutritional manipulations might be a way of significantly increasing N utilization and decreasing N pollution by dairy cows, and where as protein sources are expensive so, the cost of diet decrease (Castillo et al., 2001). The objective of this study was to examine the product and component of milk of dairy cows offered diets with different ratios of ERDP/FME.