Over recent years there has been increasing interest in the diversity of materials which may be used as energy sources in dairy cow concentrates. Traditionally, many dairy concentrates have been based upon cereals with the cereal starch providing a rapidly fermentable energy source. Such diets, particularly on systems where the feeding frequency is low, may depress rumen pH and promote low rumen volatile fatty acid ratios of acetic + butyric : propionic which are associated with the production of milk of low fat content. The feeding of dairy concentrates based upon materials containing appreciable quantities of digestible fibre may be expected to alleviate this problem. The purpose of the trial reported here was to investigate the effect of concentrate energy source on lactation performance of dairy cows.

30 autumn calving multiparous Friesian cows were fed one of two concentrates which were formulated to isoenergetic extremes of starch and fibre content.

Three weeks before their expected calving date cows were housed in cubicles with access to Calan individual feeders. Following equalised concentrate feeding in a post-parturn covariance period, one of each pair (Pairing having been on the basis of previous milk yield, milk composition and expected calving date) was gradually introduced to its designated concentrate over a five day period. Cows were flat rate fed at 7, 10 or 13 kg concentrate DM/d (depending upon yield potential) from day 20 of lactation for 10 weeks. Concentrates were fed in three equal feeds daily.