Effects of mild food deprivation on the estrous cycle of rats

It has long been known that severe food deprivation disrupts the estrous cy cle. One of the main problems with behavioral tasks that use food for reinf orcement is the requirement that the animal be food deprived. This manipula tion could be problematic in studies using female animals, since it may int erfere with the estrous cycle of the animals. The purpose of the present st udy was to investigate: (1) the effect of mild food deprivation on four dif ferent strains of rats, (2) factors in the food deprivation procedure that could affect the estrous cycle, and (3) the possible effect of enriched die ts during food deprivation on the estrous cycle. A comparison of the estrou s cycle in four different rat strains revealed differences in the reliabili ty of the estrous cycle even before the onset of food deprivation. Fischer, Long-Evans, and Sprague-Dawley rats all showed reliable cycle patterns. Th is was not the case for Brown Norway rats. During food deprivation, the cyc le of the Fischer rats was disrupted, whereas the Long-Evans and Sprague-Da wley animals continued to cycle. Both the rate of weight loss and the perce nt of ad libitum body weight were related to cessation of the estrous cycle . However, enriching an animal's diet with sugar or oil additives delayed t he disruption of the estrous cycle. Additionally, animals resumed cycling w hen returned to ad libitum weight levels. The present findings suggest that when animals need to be food deprived, preference should be given to using Long-Evans or Sprague-Dawley rats. If Fischer rats must be used, they shou ld not be deprived below 90-95% of their ad libitum body weight. Strategies for future food deprivation studies are discussed, as well as a comparison of the effects of mild and severe food deprivation. (C) 2001 Elsevier Scie nce Inc. All rights reserved.