Previous studies at this Institute have shown a marked interaction between level of supplementary feeding and protein content in the supplement with dairy cows offered high quality grass silage-based diets. For example, a given milk yield or yield of milk constituents can be obtained by offering supplements of high crude protein (CP) content, eg 340 g CP/kg fresh weight, at much lower levels than would be required with conventional supplements with a CP content of 180 g/kg fresh weight. The aim of the present study was to quantify if. the interrelationships established with high digestibility silages also applied with lower digestibility silage.

The experiment was carried out with 60 autumn-calving British Friesian dairy cows. Twenty eight animals were offered early cut silage (E), harvested between 17-19 May, with the remaining thirty two animals offered late cut silage (L) harvested between 2-12 June. Both E and L silages were produced from the same swards and in both cases grass was direct harvested and treated with an inoculant of Lactobacillus plantarum, at the rate of 3.0 litres/t fresh herbage.