Buchanan, J. S.*; Cranford, J. A.: Changes in energy utilization, food processing, and gastrointestinal morphology of voles under differing environmental conditions

Meadow voles (Microtus pennsylvanicus) are small herbivores that are active year-round, yet have no capacity for torpor. Their food supply, though abundant, may be of low quality when plants undergo winter senescence. Therefore, they must adjust their food intake rate and/or modify their gastrointestinal morphology in order to obtain the energy necessary to meet increased demands during winter. We performed an experiment of factorial design, consisting of 112 meadow voles, each assigned to one of eight trials, placed under the conditions of high (50% NDF) or low (5% NDF) dietary fiber, high (21 C) or low (5 C) temperature, and long (16L:8D) or short (8L:16D) photoperiod to determine which of these environmental variables was most responsible for eliciting the behavioral or morphological changes required for meadow voles to survive the winter. Meadow voles increased food intake and decreased dietary turnover time under the most demanding environmental conditions. Consequently, they were able to compensate for their increased energy demands by increasing food intake and decreasing dietary turnover time, and made only minimal changes to their gastrointestinal morphology. Dietary fiber level was the most important factor in eliciting these changes in intake rate, followed by ambient temperature and daylength, respectively. There were significant interactions between the three factors and all play an important role in bringing about the changes necessary for meadow voles to endureharsh winter conditions.