There is currently increasing interest in the diversity of materials which may be used as energy sources for dairy cow diets. Feeding of concentrates with a high “digestible fibre” content may be of benefit to the lactating dairy cow. In comparison with a concentrate based on a highly fermentable energy source such as cereal starch a concentrate high in digestible fibre content may undergo a slower fermentation within the rumen such that the resultant fermentation pattern may be altered. Diets and feeding regime's that promote low rumen volatile fatty acid ratios of acetic plus butyric:propionic have been associated with the production of milk of low fat content. Feeding of a high “digestible fibre” concentrate may therefore help prevent this problem. The purpose of the trial reported here was to compare the effects of concentrate energy source on the milk performance of dairy cows in early lactation.