1. Oxygen consumption and Na+,K+-ATPase(EC 22.214.171.124)-dependent (ouabain-sensitive) and -independent respiration were measured for duodenal mucosa biopsies from 10-month-old sheep given two levels of digestible energy (DE) intake (7.6–7.7 and 14.8 MJ lucerne (Medicago sativa) pellets/d) and following 48 h of starvation.
2. The mucosal biopsies were determined to be structurally intact and free of adherent bacteria on histological and scanning-electron-microscope examinations.
3. The use of D-glucose as a substrate during incubations did not elevate (P > 0.05) the respiration indices of the biopsies over those measured during acetate incubations.
4. Glucose uptake did not (P > 0.05) influence the Na+,K+-ATPase-dependent respiration of the mucosal biopsies.
5. Na+,K+-ATPase-dependent respiration accounted for 50% of the total O2, consumption of the mucosal biopsies of sheep given the lower level of DE.
6. Total O2, consumption of the duodenalmucosa was not (P > 0.05) increased when sheep were given the higher level of DE but Na+,K+-ATPase-dependent respiration of the mucosa was elevated (P < 0.01) by 37% during this period.
7. When sheep were starved for 48 h, total O2, consumption of the mucosal biopsies was not (P > 0.05) affected, however, Na+,K+-ATPase-dependent respiration of the biopsies dropped (P < 0.01) by 45%.
8. Na+,K+-ATPase-dependknt respiration accounted for 61.3% of the O2, uptakes of mucosa from the sheep given the higher level of DE and 28.3% of the 02, uptake of mucosa from fasted sheep.