The objective of this study was to evaluate whether the monensin concentration affects DMI, rumen fermentation, short-chain fatty acid (SCFA) absorption across the rumen and total-tract barrier function. Four ruminally cannulated Hereford × Angus heifers were used in a 4 × 4 Latin square design with 24-d periods. Heifers were fed a barley-based finishing diet (76% rolled barley grain, 12% barley silage, 8% mineral and vitamin supplement, and 4% canola meal) containing either 0, 22, 33 or 48 ppm monensin. Urinary recovery of Cr-EDTA was used as an indicator of total-tract barrier function (d 18 to 20). Days 20 to 23 were used to evaluate rumen fermentation and total-tract digestibility measurements, and SCFA absorption was measured on d 24. Data were analyzed using PROC MIXED of SAS with linear and quadratic contrasts. Increasing monensin inclusion decreased DMI linearly (10.0, 9.9, 9.3, and 9.1, kg/d DM respectively, P = 0.01), but as the dose of monensin increased, BW, ADG and G:F ratio were not affected (P ≥ 0.11). Total Cr-EDTA recovery was not (P ≥ 0. 61) affected by increasing dose of monensin, nor was rumen pH (mean, minimum, maximum, duration <5.5, area under curve; P ≥ 0.21). The acetate-to-propionate ratio decreased linearly (1.9, 1.8, 1.4, 1.3, respectively, P = 0.03) as dose of monensin increased. A quadratic response (35.7, 47.5, 41.8, 35.4%, respectively, P = 0.02) for the absorption of acetate was detected with a maximal value at 22 ppm. Ethanol soluble carbohydrate digestibility increased linearly (77.2, 84.7, 88.0, 94.0%, respectively, P = 0.003) with increasing doses of monensin. Starch digestibility showed a quadratic response (93.8, 93.9, 88.0, 94.0%, respectively, P < 0.001), where 33 ppm inclusion had a minimal value. The results from this study indicate that increased monensin inclusion decreases DMI without affecting SCFA concentrations, SCFA absorption, and total-tract barrier function.