The effect of protein, energy and phosphorus supplements, fed individually or in various combinations, on roughage intake and livemass change was measured in a 2 x 2 x 2 factorial arrangement of treatments. The experiment was conducted under controlled conditions designed to simulate conditions which exist in practice when animals are fed supplementary licks on winter grassveld. The level of supplementary feeding was designed to supply 60%, 10% and 50%, respectively, of the animals' daily requirements for protein, energy and phosphorus in the form of the supplement only. Protein supplementation, averaged for all treatments, increased roughage intake 34,5% over the non-supplemented groups. Protein supplemented cattle also lost only 4,7 kg livemass whereas the groups not receiving protein lost an average of 19,6 kg. In marked contrast to protein, low-level energy supplementation had an insignificant, small positive effect on both feed intake and livemass change except where it was given as the only supplement and where it had a negative effect on animal performance. Phosphorus supplementation, except where it was given in combination with both protein and energy, tended to have a negative effect on both feed intake and livemass change. The response to protein was only slightly enhanced by combining protein lick with both energy and phosphorus supplements. This experiment shows that a protein deficiency is by far the most important cause of winter mass loss in cattle maintained on low-quality forages.