An experiment was conducted to investigate the effects of supplements of sorghum grain (1·1 kg/day), sodium propionate (65 g/day) and intra-abomasal glucose infusion (200 g/day) on the liveweight gain (LWG), glucose metabolism and nitrogen utilization of Hereford steers (four per group) given molasses-based diets ad libitum (molasses 589, urea 18, sunflower meal 194, pangola grass hay 187, minerals 12 g/kg as fed). There was no significant effect of treatment on voluntary feed consumption (97–106 g dry matter (DM)/kg0·75 per day) or DM digestibility (0·564–0·579). The LWG of steers given grain supplements (899 g/day) and sodium propionate (943 g/day) were significantly (P<0·05) higher than those of steers given the basal diet (741 g/day) and basal diet plus glucose infusion (794 g/day).

All supplements decreased plasma urea concentrations and urinary N excretion and increased the efficiency of N utilization from 0·19 to 0·36–0·38 g N retained per g apparently digested N intake. The provision of grain (13% DM intake) increased ammonia and volatile fatty acid (VFA) concentrations in rumen fluid, and both grain and sodium propionate increased the proportion of propionic acid in ruminal VFA. Grain supplementation and glucose infusions significantly (P<0·05) increased glucose entry rates (g/day and g/kg0·75 per day) without affecting plasma glucose concentrations or glucose pool size and space. Sodium propionate supplements increased plasma insulin concentrations to a lesser extent than grain supplements and glucose infusion. Increased glucose availability in the present studies was associated with an improved utilization of dietary protein and, in some cases, with improved LWG.