The addition to grass during ensiling of enzymes capable of hydrolysing forage polysaccharides has been shown to result in increased fermentation of dry matter within the silo (Jacobs & McAllan, 1987). Thus it appears that the enzymes promoted cellular breakdown within the silo. It is also possible that the enzymes may also have made available greater amounts of structural carbohydrate for utilisation within the rumen. Such an increase in available energy may be reflected in improved microbial activity in the rumen resulting in increased microbial protein synthesis. The present experiment examines the effects of enzyme treated silages on the flow of nitrogenous constituents at the duodenum of growing steers.