The efficiency of nitrogen (N) utilisation in dairy cows fed grass silage diets is normally low and is related to an impaired utilisation of N in the rumen. Choice of carbohydrate type may affect this efficiency, influencing milk production and composition, and changing the output of N in faeces or urine. This experiment was undertaken to examine the effect of different iso-energetic supplements containing contrasting energy sources on N utilisation and milk production in early/mid lactation dairy cows fed early cut partially wilted grass silage.
Six iso-energetic supplements were formulated as treatments; four to contain 160 g CP/kg DM and contrasting carbohydrate sources, viz.: neutral detergent fibre (NDF; wheatfeed, 350 g/kg, molassed and unmolassed sugar beet pulp 412 g/kg); low degradability starch (LDS; maize grain 500 g/kg, wheat 237 g/kg); high degradability starch (HDS; wheat and barley grain 812 g/kg); and soluble sugars (SS; molasses, 525 g/kg, citrus pulp, 125 g/kg).