The objective of this experiment was to compare net nutrient absorption and oxygen consumption by portal-drained viscera (PDV) of catheterized Holstein steers (333 kg) when fed alfalfa or orchardgrass silage at two equalized intakes. The design was a 4 X 4 Latin square with a 2 X 2 factorial arrangement of alfalfa or orchardgrass fed at 65 or 90 g dry matter/kg.75 live weight daily. Blood flow through PDV (dilution of p-aminohippurate), net nutrient absorption and oxygen consumption (venoarterial concentration differences times blood flow) were measured hourly for 12 h, followed by measurement of N and energy balance over 7 d. Compared with orchardgrass, steers when fed alfalfa absorbed more NH3-N (P less than .05), branched-chain volatile fatty acids (P less than .10) and n-valerate (P less than .05). Silage type did not affect (P greater than .10) blood flow to or O2 consumption by PDV or net absorption of glucose, L-lactate, acetate, propionate, urea-N, alpha-amino N or most amino acids. Oxygen consumption by PDV as a percentage of whole-animal O2 consumption was not different (P greater than .10) for steers when fed orchardgrass (27.2) or when fed alfalfa (23.6). Interrelationships between N and energy metabolism were responsible for the increased (P less than .05) metabolizable energy/kilogram silage dry matter and increased (P = .10) N retention by steers when fed alfalfa compared with orchardgrass. The PDV accounted for a substantial portion of whole-animal O2 consumption.