When concentrate allowance is changed the allowances of both energy and crude protein change. In this experiment, which was part of a larger series, concentrate energy supply was increased at a constant supply of crude protein.

Sixteen Ayrshire and Friesian cows were given either 4kg/d of a high protein concentrate (321g/kg DM), T4, or 8kg/d of a low protein concentrate (173g/kg DM), T8, as well as ad. libitum access to silage through Calan-Broadbent gates (pH 3.8, DM 220g/kg, ME 10.1 MJ/kg DM, CP 147g/kg DM, NH3-N 43g/kg total N). There were two periods of 8 weeks starting three weeks after calving. Performance in week two was used as a covariate. The treatments in the two periods were: T4/T4, T4/T8, T8/T4 and T8/T8. Milk yields and silage intakes were recorded daily; milk composition was measured weekly and cows were weighed twice weekly by weighband.