RESPONSES OF THE GUT TO MODERATE ENERGY DEMANDS IN A SMALL HERBIVORE (MICROTUS-PENNSYLVANICUS)

The objective of this study was to determine compensatory responses of the gut to moderate increases in energy demand in the meadow vole (Microtus pennsylvanicus). Energy utilization and gut characteristics of voles with elevated metabolic rate, and thus, elevated energy demand were compared to those of voles with non-elevated energy demands. Food intake increased by 40% with increased energy demand while turnover time of digesta decreased by 26%. Despite shorter turnover time and a 4% loss of digestive efficiency, digested energy increased by 30%. The major changes of the gut that occurred with elevated energy demand were increases in the wet and dry mass of the small intestine, specifically that of the mucosal layer, and the wet and dry mass of the caecum. There were no significant changes in the mass of the stomach or colon. In contrast to studies with more extreme increases in energy demand, there was no change in the length or circumference of any gut organ. We propose that moderate increases in nutrient utilization are accomplished through proliferation of existing gut tissue, particularly mucosal tissue, without the cost of producing additional length of gut organ.