Ten Dohne merino wethers with an average mass of 50 kg were used to study differencesin the use of energy by the splanchnic tissues and their metabolism of VFA, glucose and FFA when fed high- or low-fibre diets. Dietary carbohydrate was provided in either the structural (HF treatment) or readily fermentable form (LF treatment), while energy and nitrogen intakes were kept constant. The wethers were fitted with ruminal cannula and with catheters in the abdominal aorta, mesenteric, portal and jugular veins. All 10 sheep were subjected to two protocols, separated by at least 2 weeks to minimise carry-over of isotopes. Either (1-14C)-acetate or (2-14C)-propionate as continuously infused into the rumen concurrently with either (9,10 N-3H)-FFA or (6-3H)-glucose into the jugular vein. Blood and digesta samples were drawn simultaneously after plateau specific radioactivities of these metabolites had been achieved. The effective tissue energy use by the PDV was higher (p < 0.05) for the LF than for the HF diet (60.9% vs. 57.9%). The PDV used between 20 and 27% of digestible energy intake and differed (p < 0.05) between groups. The net flux of propionate and FFA across the PDV were higher (p < 0.05) for the LF than the HF treatment. PDV utilization and production differed (p < 0.05) between treatments for all metabolites. The net hepatic flux of acetate and FFA was higher (p < 0.05) on the HF than the LF treatment. Production by the liver differed (p < 0.05) between treatments for all metabolites. It appears that glucose and propionate metabolism shifted away from the liver to peripheral tissues when the LF diet was fed. In general, the peripheral metabolism of acetate and FFA differed significantly (p < 0.05). The net utilization of acetate and FFA, as well as the conversion of acetate to FFA, was higher (p < 0.05) on the HF than on the LF diet. The results of this study show that, while the PDV and liver play a central role in the partitioning of absorbed nutrients between various metabolic pathways, the difference in the efficiency of dietary energy utilisation remains to be fully explained.