Limits to food intake by the Prairie Vole: effects of time for digestion

1. Prairie Voles (Microtus ochrogaster Wagner) are among the smallest vegetation-feeding mammalian herbivores, and thus show a high ratio of energetic expenditure to energy content of ingested food that may lead to digestive bottlenecks. By varying the periodicity of 3 h of food availability, it was found that energy assimilation in Prairie Voles is not limited by the time required to consume food, but by the time required to digest and absorb food. 2. Three hours is all the time that is necessary for a Prairie Vole to consume the food needed for I day. Although voles offered food in one 3-h block per 24 h increased dry matter digestibility, they could not consume enough food to maintain body mass. However, when offered 3 h of food availability but divided into six 30-min periods evenly spaced throughout 24 h Prairie Voles reached a level of food intake similar to that of control voles fed ad libitum and stabilized body mass similar to controls. 3. It is suggested that a vole's stomach capacity limits intake for each feeding bout, regardless of how empty the following chambers are after any period of food restriction and the rate of stomach emptying may dictate the feeding bout periodicity. The amount of stomach contents (1.1-1.4 g) found in voles held under similar conditions to those in our experiments closely resembles the amount of food consumed (0.78-1.4 g) during each of the six 30-min periods of feeding. 4. The bottleneck limits intake of food and keeps feeding bouts spaced. The time required for digestion may be the cause for a vole's observed 2-4 h ultradian activity rhythm. Evidence is given that spacing between activity periods may be adjusted to the metabolic demands of the species.