Previous studies at this Institute have shown that there is an interaction between level of supplementary feeding and protein content in the supplement. For example, a given milk yield can be obtained by offering supplements of high crude protein content at much lower levels than would be required with conventional supplements. Furthermore, this approach enables a greater reliance on the forage component of the diet, particularly where high quality grass silage is available. The objective of the present large scale study was to determine milk production responses to supplements of differing protein content, given with high quality grass silage, and to examine effects on ration digestibility.

The experiment was carried out over a two year period, with a total of 168 autumn-calving British Friesian dairy cows. Supplements containing either 100, 220, 340 or 460 g crude protein (CP)/kg fresh weight were offered from day 14 of lactation. Each supplement was offered at four levels, with 9 animals per treatment.