SUMMARY
When female mice were caged in groups of thirty, regular oestrous cycles did not occur in the majority of animals. The vaginal smears of these mice were mucified and some remained so for 40 days. Cycles promptly returned when the mice were caged individually.
The ovaries of the grouped mice were significantly lighter than those of individually housed controls, although the body weights were not different. Fewer of the grouped animals had tubal ova and corpora lutea were absent from, or atrophic in, some of the ovaries.
A decidual reaction was obtained in only one of ninety animals following trauma of the endometrium.
When grouped mice were subsequently paired, mating occurred 3 nights later in 53%. When females were caged singly the occurrence of mating was distributed more evenly over the first 4 nights.
Regular oestrous cycles did not occur in blind mice while they were grouped or in mice when they were separated by partitions in the cage.
It is concluded that anoestrus occurs when mice are grouped and results from a depression of pituitary gonadotrophic function. This depression is independent of mutual visual or tactile stimuli.