Technical Abstract: Several researchers have investigated cattle supplementation strategies, yet few studies focused on the benefits of supplementation time on herbage utilization. Using a dual flow continuous culture fermenter system designed to simulate ruminal digestion and nutrient outflow to the intestines, this study evaluated the effect of maize silage supplementation, either 9 or 1 h before a hypothetical herbage meal, on ruminal digestion and nutrient flows. Fermenters were operated four 10 d periods (7-d adaptation, 3-d sampling). Treatments were: feeding maize silage 9 (9BH) or 1 h (1BH) and control (CTL, no feeding of maize silage), before a single herbage meal. Herbage was fed as follow; 66% of the total herbage meal (1600 h), 22% (1720 h) and the remaining 22% at 1840 h. Maize silage was fed at 40% (dry matter (DM) basis) of the total diet. Effluent was analysed for organic matter (OM), crude protein (CP) and neutral detergent fiber (NDF). Purine concentrations in effluent and bacterial isolates were used to partition effluent N flow into bacterial and non-bacterial fractions and to calculate true OM digestibility and flows. Fermenters were sampled for pH, volatile fatty acids (VFA) and NH3-N at 0730, 1100, 1530, 1600, 1720, 1840 and 2000 h. Data were analysed as a 3 × 4 Latin rectangle. True OM (mean 61.1 %) and CP (mean 84.6 %) digestibilities were not affected by treatment. Apparent NDF digestibility was the highest for CTL (84.4%) and the lowest (78.1 %) for 9BH. Treatment affected NH3-N (18.7, 8.8 and 11.4 mg/100ml for CTL, 9BH and 1BH, respectively), bacterial efficiency (19.6, 17.6 and 15.4 g N/kg OM truly digested for CTL, 9BH and 1BH, respectively) and effluent of NH3-N (0.42, 0.019 and 0.26 g N/d for CTL, 9BH and 1BH, respectively). Treatments did not affect effluent of dietary N (0.32 g/d at mean), nor total VFA and acetic acid (91.3, 44.9 Mmol/ml at mean; P = 0.09). Propionic acid was greatest for 9BH. The pH was the highest for CTL and the lowest for 9BH (6.6 and 5.6, respectively). Strategically timed maize silage supplementation (9BH) improved bacterial efficiency, N utilization and supplied more glucogenic nutrients. A simple change in timing of supplementations may improve herbage utilization, while probably reducing environmental impact.