Studies reported by Mayne (1990) and Slater (1989) have shown that the yield of milk achieved by feeding a low level of a high protein concentrate with a good quality silage fed to appetite was comparable to that obtained by feeding higher levels of a conventional concentrate containing a normal level of protein (160-180g CP/kg). These results would indicate that there is considerable scope to reduce concentrate feeding levels and reduce feed costs when good quality grass silage is available. However, in previous studies at this centre (Murphy, 1987) very low levels (2.4 kg/d) of high protein concentrates (400-450 g CP/kg) fed with a good quality grass silage reduced milk production compared with a moderate level (6 kg/d) of a normal protein concentrate (160-180 g CP/kg).

The present study was carried out to clarify the position and to establish the benefit of including a source of undegradable protein, e.g. maize distillers grains or fishmcal in place of soyabcanmeal in the prolein concentrate.