The purpose of the experiment was to evaluate the effect of long-term feeding of bulls with a diet containing condensed beet molasses solubles (CBS) supplemented with MgO (10 g/kg CBS) on growth, blood and rumen content indices. The experiment was conducted on 48 crossbred bulls from an initial weight of 148 kg to a slaughter live-weight of 400 kg. Approximately 40% of the concentrate in the experimantal diet was replaced with CBS. Average body gains were 852 and 804 g/d in the control and experimental groups, respectively, but did not differ significantly. Long-term feeding with a CBS-containing diet did not disturb rumen and tissue metabolism and had no effect on carcass composition and chemical composition of the longissimus dorsi muscle.