Homeostatic competition in rats fed at varying distances from a thermoneutral refuge

Rats were fed in an air temperature of -15 degrees C at distances of 1, 2, 4, 8 or 16 m from a thermoneutral refuge. As the distance between the feeder and thermoneutrality increased, the number of excursions to feed decreased from 37 +/- 5 to 7 +/- 1 during the 2-hour feeding sessions; concomitantly, the meal duration increased from 1.2 to 5.2 min. The rate of eating and total feeding time were the same at all distances. The mass of food ingested was also constant except for a slight decline at 16 m. Meal duration was strongly correlated (r = 0.9) with the time taken to reach the feeder at each distance while the estimated cost/benefit of feeding episodes increased with distance. Estimates of body temperature indicated that significant falls in skin temperature occur over even short distances, while over greater distances core temperature probably also decreases. In the range of distances studied, rats accorded their hunger drive a higher priority than thermal preference, and chose to feed while tolerating greater thermal disturbance.