There is now a considerable volume of evidence to indicate that, with high quality, grass silage-based diets, good animal performance can be achieved by offering supplements of high crude protein content at much lower levels than would be required with conventional supplements. Given the current constraint on milk output at farm level, there is considerable interest in lower cost milk production systems and high protein supplements would appear to have a role to play in this context. However, there is little information available which enables prediction of milk yield responses to increasing levels of supplements of differing protein content. The objective of this study was to determine response curves to supplements of differing protein content, given in addition to grass silage, thereby facilitating a least-cost diet type approach to achieving a given level of milk output.

Concentrates containing either 100, 220, 340 or 460 g crude protein (CP)/kg fresh weight were offered to 72 autumn-calving dairy cows from day 14 of lactation, with each concentrate offered at four levels of feeding.