The objective of this trial was to evaluate rumen fermentation, N metabolism and ingestive behavior of cattle fed diets containing flint corn (70 – 75% vitreous endosperm) either ground at 2.70 mm or steam-flaked at 360 g/L, combined with dietary contents of 4, 7, 10 or 13% (DM basis) NDF from sugarcane bagasse. Sixteen Nellore bulls (484.46 ± 7.47 kg) fitted with rumen cannula, were fed diets containing 76–86% corn and randomly allocated to 16 pens for 2 periods (14d adaptation; 6d collection) in a 2 × 4 factorial arrangement. During the collection period the amount of diet offered once a day was restricted to 85% of previous ad libitum intake. Rumen samples were collected on d 16 at 0, 2, 4, 6, 8, 10, 12, 16 and 24 h post feeding. Blood samples and urine spot samples were collected on d 15, 4 h post feeding. Microbial synthesis was estimated based on the purine derivative method. The data were analyzed using a PROC MIXED model with period and animal as random effect. Linear and quadratic effects were tested for dietary concentrations of roughage NDF. No interactions were observed between corn processing and NDF level. Steam-flaking increased (P < 0.01) rumen propionate and decreased (P < 0.01) butyrate and N-NH₃ concentrations. Steam-flaking decreased (P < 0.01) N ingestion, blood urea nitrogen (BUN), N urine and total N excretion and increased (P = 0.03) microbial efficiency. Increasing dietary sugarcane bagasse NDF tended to increase linearly (P = 0.10) rumen pH and decreased linearly (P = 0.05) rumen propionate and (P = 0.05) total VFA. Increasing bagasse NDF caused a quadratic effect (P < 0.01) on N ingestion and absorption. Rumination and mastication time were increased linearly (P < 0.01) as roughage NDF was increased. Blood glucose and BUN were not affected (P = 0.53 and 0.54, respectively) by bagasse NDF level. In conclusion, steam-flaking of flint corn improves energetics and N metabolism of beef cattle. Feeding increasing levels of bagasse NDF stimulates rumination but it decreases the efficiency of energy production in the rumen.