The study was conducted to examine the response of dairy cows to changes in sources of dietary starch and to investigate whether ‘root’ starch sources are comparable to cereal starch sources in terms of the performance of lactating dairy cows.

Thirty multiparous British Friesian/Holstein lactating diary cows, in a randomised block experiment, were allocated to one of five dietary treatments containing different proportions (1.00:0.00, 0.75:0.25, 0.50:0.50, 0.25:0.75 and 0.00:1.00), respectively, of two dairy concentrates (C or R) which were formulated to the same crude protein (180 g/Kg), ME (11.5 MJ/Kg FM) and starch (300 g/Kg) levels but differing only in the principal sources of starch. Barley and wheat were the principal sources of starch in the ‘cereal’ starch source concentrate (concentrate ‘C’) whilst cassava was the main ingredient in the ‘ root ’ starch source concentrate (concentrate ‘ R ’). All cows were offered the concentrate diet on a flat rate (10 Kg FM/day) with grass silage fed to appetite.