High producing dairy cows are often fed large quantities of high quality proteins, and because ruminal protein degradation is not directly coupled to microbial protein synthesis, ruminal NH3-N production is always excessive and ultimately lost by urinary N excretion. Increasing the supply of ruminally fermentable carbohydrates can reduce ruminal ammonia-N concentration and increase milk protein yield (Sannes et al., 2002). The addition of sugar has increased ruminal and whole animal N efficiency in sheep and steers, reportedly to a greater extent than starch (Chamberlain et al., 1993). The objective of this work was to investigate the effect of diets containing different non fibre carbohydrates (NFC, sucrose or starch) on ruminal pH and ammonia-N concentration in Holstein steers.