Crossbred catheterized wethers (20 months old; 45 kg BW, SE 0.7) consumed ad libitum warm ((W) bermudagrass;Cynodon dactylon ) or cool ((C) ryegrass-wheat mixture; Lolium multiflorum and Triticum aestivum, respectively) season grass hay with 0%, 20% or 40% legume hay ((L) alfalfa; Medicago sativa). Legume, W and C had 54%, 80% and 68% NDF and 17%, 14% and 10% CP, respectively (DM basis). Apparent digestible energy intake was 3.22, 3.42, 3.66, 3.23, 3.57 and 3.67 (SE 0.208) Mcal day - 1 , and apparent digestible N intake was 17.6, 20.2, 23.4, 10.1, 14.0 and 17.3 (SE 1.09) g day - 1 for W:0% L, W:20% L, W:40% L, C:0% L, C:20% L and C:40% L, respectively. Splanchnic bed oxygen consumption (306, 364, 380, 261, 316 and 383 mmol h - 1 ; P = 0.02) and portal-drained viscera (PDV) releases of alpha-amino N (24.8, 37.6, 38.6, 24.4, 38.4 and 41.7 mmol h - 1 ; P = 0.04) and propionate (14.4, 19.4, 20.5, 14.3, 23.6 and 21.1 mmol h - 1 for W:0% L, W:20% L, W:40% L, C:0% L, C:20% L and C:40% L, respectively; P = 0.08) were greater with L than without. However, splanchnic bed net releases of alpha-amino N and glucose were similar among treatments. In conclusion, dietary L inclusion had similar effects on splanchnic tissue oxygen consumption and net fluxes of nutrients regardless of grass source, which differed in concentrations of NDF and CP but not in apparent digestible energy intake. These results suggest that potential improvement of animal performance by substituting 20% or 40% legume for warm or cool season grass, consumed ad libitum by mature ruminants, would not be attributable to change in extra-splanchnic tissue availabilities of energy (based on the difference between apparent digestible energy intake and splanchnic tissue energy consumption), amino acids or glucose.