AbstractIntake in sugar-rich diets can be limited either via rumen fill or excessive rumen fermentation and source of non-fibre carbohydrate (NFC) in the diet can affect both factors. The aim of the current study was to quantify the effect of partially replacing ground maize (GM) with steam-rolled maize (SRM) or pelleted citrus pulp (PCP) at two concentrate levels in sugarcane-based diets on digestibility, rumen ecosystem and metabolism of Nellore steers. Six rumen-cannulated steers were assigned to a 6 × 6 Latin square, replicated in time, in a 2 × 3 factorial arrangement of treatments with two levels of concentrate (600 or 800 g concentrate/kg dry matter [DM]) and three NFC sources. Each steer within a period was considered an experimental unit. Feeding more concentrate increased total tract digestibility of organic matter and decreased fibre intake and passage rate. It also reduced rumen populations ofFibrobacter succinogenesandStreptococcus bovisand increasedRuminococcus flavefaciens. Substituting PCP for GM increased rumen pH, acetic acid and organic matter digestibility. Feeding PCP also reducedR. flavefaciensandR. amylophilusrumen populations. Substituting SRM for GM increased starch digestibility and rumen propionic acid, but decreased rumen ammonia concentration. Feeding SRM increased rumen populations ofMegasphaera elsdeniiwith the high-concentrate diet but reducedRuminococcus albuspopulations at both concentrate levels. In conclusion, partial replacement of GM by PCP decreased intake in sugar-rich diets, while increasing total tract neutral detergent fibre digestibility. Replacement of GM with SRM increases rumen fermentation and total tract digestibility of starch.