To investigate the role of food intake in seasonal body weight changes in the Djungarian hamster, we divided animals, which had minimum body weights after 18 wk in SD, into ad-lib feeding and restricted feeding groups under a long day (LD) and a short day (SD) photoperiods. In the ad-lib feeding groups, body weight and food intake increased in parallel after 3 wk under LD and after 6-7 wk in SD because of photorefractoriness. In the restricted feeding groups, almost all animals moved around furiously (food-seeking activity) when they came to consume all the food provided at 2-3 wk of the treatment in LD and after several weeks in SD with the initiation of photorefractoriness, and ended up with death. In the restricted feeding groups, body weight increase was not observed. The furious food-seeking activity in the restricted groups and the increase of body weight specific food intake (food intake/body weight) in the ad-lib feeding groups might reflect the increased requirement for food. This increase of requirement for food seems to be one of the critical factors regulating the seasonal body weight change.
