Submitted to: European Association of Animal Production Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: September 15, 2000
Publication Date: N/A
As much as 25% of the energy consumed by the ruminant animal is oxidized by the tissues of the portal-drained viscera. Although studies in vivo have demonstrated that specific energy substrates are used extensively, limited information is available relating to substrate specificity and extent of substrate use by ruminant gut tissues. Therefore, the objectives were to investigate glucose metabolism by isolated duodenal enterocytes from steers and to develop accurate estimates of the affinity for and the extent of glucose oxidation by ruminant enterocytes. Steers were fed a common corn silage based diet ad libitum for at least 28-d prior to slaughter. At slaughter, duodenal tissue was collected and cells were isolated by collagenase digestion for analysis of glucose oxidation using 60 min incubations in vitro. Treatments included glucose alone (.001 to 30 mMoles/L) or glucose with additional energy substrates and metabolic hormones. Glucose (3 mMolar) oxidation to CO2 was linear over time for each animal, with R2 ranging from .77 to .92. Glucose dose response data were used to develop kinetic parameter estimates, Vmax and Kox, using the equation: Y = Vmaxù(conc/ (Kox+conc)) in which Y= metabolite produced or substrate oxidized to CO2 (nMoles / 60 min) and conc = initial flask substrate concentration. The fit of the equation to the data resulted in R2 ranging from .79 to .91. Estimates of Vmax and Kox for glucose oxidation to CO2 are calculated to be 5.44 and 3.04, respectively. These values are three- to five-fold lower than we have previously observed for rumen epithelial cells. Results of further ongoing experiments, designed to test the effects of additional substrates and specific hormones, will also be presented.