The trial is one of a series in a project to develop a mathematical model to predict the consequences of changes to the food supply on yields of milk constituents. The objective of the trial was to measure the responses of winter-calved dairy cows to changes to the level or to the distribution within a level of concentrates given with grass silage ad libitum.

Ninety-eight British Friesian cows in their second or subsequent lactations with a mean calving date 6 December were used in a randomised block experiment. There were 7 treatment groups. Cows received on average 3, 6 or 9 kg concentrate dry matter (DM) per day over weeks 4 to 22 of lactation.