Suppression of Oestrus in Grouped Mice: The Effects of Various Densities and the Possible Nature of the Stimulus

Summary. The effects of various degrees of grouping on the oestrous cycle of C57BL/6 and BALB/Ci mice were examined. The results support the findings of others which have shown that suppression of oestrous occurs as a result of female grouping and indicate that oestrus can be suppressed by housing females even in pairs. Strain differences were found in the oestrous response to grouping and in the density at which maximum suppression occurred. In both strains, the suppression took the form of a relative lengthening of the dioestrous phase of the cycle. A second study revealed that the effects of grouping on the oestrous cycle could be imitated by housing single females in cages recently soiled by groups of females, and suggested that a pheromone may be the stimulus for suppression.