There has been much recent debate about the protein requirements of lactatinq dairy cows, and this issue has been heightened by a general reduction in concentrate feeding in response to the imposition of milk quotas. Furthermore, the value of silage as a source of protein has been questioned widely. The objective of the present trial was to determine the effect of increasing supplementary protein on the performance of cows with ad libitum access to high quality grass silage.

The trial, using January/February calving British Frieslan cows in second or subsequent lactations, was performed at Ravenscroft Hall Farm, Middlewich, Cheshire. Four groups of 15 cows were offered either 3 or 6 kg/head/day of cereal/soya/fishmeal based compound feeds containing either 214 (L) or 403 (H) g CP/kg DM, and high quality grass silage ad libitum.