Carbohydrate not recovered in NDF is referred to as nonfibre carbohydrate (NFC) and includes starch, sugars, pectins and beta glucans. The optimal level of dietary NFC for lactating cows is not clearly defined. It has been demonstrated that milk production was decreased when dietary NFC was greater than 45 to 50% or less than 25 to 30% of dry matter. However, only small differences in milk production occurred as dietary NFC was varied from 35 to 40% (Batajoo et al, 1994). Replacement of NSC with suplemental fat decreases the amount of energy that is available for growth of ruminal microorganisms and may decrease microbial protein synthesis. The quantity of fermentable carbohydrate is the single most important determinant of microbial protein production and may have a great impact on ruminal metabolism and the overall performance of dairy cows (Elliott et al, 1995). The objective of this experiment was to determine the effects of supplemental fat in concentrates containing different amount of NFC on performance of dairy cows.