Merino wethers aged 1.5 years grazed a saltland pasture comprising old man saltbush (Atriplex nummularia) with an inter-row of senesced grasses and medic for 6 weeks in autumn, in a cereal–livestock zone with a Mediterranean-type environment in South Australia. The experimental treatments were a control (old man saltbush, SB), supplementation with 250 g/sheep.day barley straw (SB + S), supplementation with 250 g/sheep.day barley grain (SB + G) and supplementation with 250 g/sheep.day barley straw + 250 g/sheep.day barley grain (SB + S + G). The sheep in SB + G finished the experimental period significantly heavier (53.6 kg, P < 0.001) than SB (51.0 kg), SB + S (50.5 kg) or SB + S + G (51.1 kg) animals. Feeding grain also increased length of wool grown daily by 16% and would have increased the value of the sheep by being able to sell them ‘out of season’ when prices are higher. Sheep supplemented with grain alone had a higher liveweight than those provided with grain and straw, a result that cannot be explained but may be associated with altered grazing behaviour. It appears that, while old man saltbush provides sheep with an acceptable intake of protein and minerals, the addition of a cereal grain supplement improves energy balance and optimises rumen protein capture to improve liveweight and wool growth performance.