The objective of this study was to evaluate the digestive characteristics of ruminally cannulated beef steers consuming a steam-flaked corn (SFC) or dry-rolled corn (DRC) based diet containing either Rumensin 90 (R) or Monovet 90 (MV). Six ruminally fistulated steers (657.7 kg 72.6) housed individually were used in a 6 6 Latin square design with a factorial treatment arrangement. Each of the 6 periods were 15 d with 14 d for diet adaptation and 1 d of rumen fluid collections. Six 15-d periods consisted of 14 d diet adaptation prior to rumen fluid collections. Dietary treatments were DRC without monensin sodium (DRC-C), SFC without monensin sodium (SFC-C), DRC with Rumensin 90 (DRC-R), DRC with Monovet 90 (DRC-MV), SFC with Rumensin 90 (SFC-R), and SFC with Monovet 90 (SFC-MV). Rumen contents and fluid were collected through the fistula of each animal at 0, 3, 6, 12, and 24 h on d 15 of each period. Rumen fluid was collected 6 h postfeeding each period for in vitro analyses. Steer was the experimental unit and the model included fixed effects of grain processing, additive, and grain processing additive. Total gas produced was composited from each in vitro bottle into a gas collection bag for the 48-h determination of methane concentration. No differences were detected for DMI (P = 0.81). Ruminal pH did not differ for the control or additive treatments (P = 0.33). However, ruminal pH was lower (P > 0.01) with SFC relative to DRC There was a significant difference in acetate to propionate ratio for both additive (P = 0.04) and grain type (P 0.01). Additive inclusion reduced methane proportion of total gas relative to control treatments (P 0.01). Monensin sodium reduced methane concentration though source had no effect on DMI or ruminal pH.