Starchy feeds favour the high protein / low fat milk that the market is increasingly demanding, though they place a considerable acid load on the rumen and there is a danger of acidosis at high levels of inclusion. The objective of the present work was to evaluate the use of maize starch, which is perceived to be more slowly and less extensively fermented in the rumen, when compared with wheat starch, in supplements for grass silage.

Thirty-two autumn-calving multiparous Holstein-Friesian cows were balanced for parity and calving date, randomly allocated to the 2 treatment groups and trained to Calan gates during the dry period. Covariance recording on a standard concentrate, was undertaken in lactation weeks 3 and 4 whilst from lactation weeks 5 to 22 cows received one of the 2 concentrate treatments (‘maize’ or ‘wheat’) in a continuous design experiment. Concentrates were fed through the Calan gates at 10 kg/day until lactation week 12 and 7 kg/day from lactation weeks 13 to 22 inclusive in two equal meals at approximately 09.30 and 16.30 h. The concentrates were formulated to be iso-energetic, iso-nitrogenous and iso-starch and balanced for minerals and vitamins. The principal starch sources were (inclusion levels in g/kg as-mixed): maize gluten (230), maize (200), maize germ (123) and barley (75) for the ‘maize’ concentrate; and wheat (425), maize germ (100) and maize gluten (100) for the ‘wheat’ concentrate.