Considerable progress has been made recently in improving the accuracy of prediction of silage intake, when offered as the sole food, to growing cattle (Steen et al, 1995). However, in order to incorporate this information into feed rationing programmes, it is essential to obtain information on how silages of differing characteristics interact when offered with a range of levels and types of supplementary feeds. The aim of this study was to examine the effects of concentrate energy source and crude protein concentration, when offered at a range of feed levels, on the voluntary food of a diverse range of grass silages with both growing beef cattle and dairy cows.