1. Three groups, each of eight steers, were fed on pelleted diets containing 30, 50 or 70% ground barley straw, maize and soya bean meal. On an air-dry basis the diets contained 12% crude protein.
2. Daily live-weight gain was 1·29, 1·19 and 1·02 kg/day for the 30, 50 and 70% straw diets respectively, and was negatively related to the percentage of crude fibre in the dry matter (r = −0·61, P < 0·05).
3. The apparent digestibility of dry matter, determined in sheep at the maintenance level of feeding was negatively related to percentage crude fibre in the dry matter (r = −0·91, P < 0·001).
4. All animals were killed at approximately the same live weight, which was reached on average in 140,153 and 163 days by the 30, 50 and 70% groups, respectively.
5. The differences in mean carcass weight between treatments were significant (P < 0·05). Killing-out percentage was significantly reduced (P < 0·05) as the proportion of ground barley straw in the diet was increased from 30 to 70%.
6. The proportion of straw in the diet had no direct effect on the composition of carcass gain.
7. The results are discussed in relation to the intake of digestible energy.