Oestrous Frequency and Incidence of Pregnancy in Mice Housed Singly and in Groups at 4, 21, and 33°C

Abstract

Oestrous cycle frequency was measured in mice housed singly, in mice housed in groups, and in grouped females in olfactory and tactile contact with a male. The animals were kept at 4,21, or 33°0. When the mice were housed singly, all groups had between 2·2 and 3·5 cycles in the 16 days period of observation. The small differences between the groups were not significant. Grouping (15 mice per cage) caused a significant reduction in oestrous frequency at all three temperatures, but the differences between the temperature groups were not significant. Introduction of a caged male into the group of females had no effect on oestrous frequency at 4 and 21 °0. At 33°0 frequency increased and the difference between the temperature groups became significant. When the males were released into the cages of grouped females the incidence of pregnancy in the group at 33°0 was seven times greater than that at 4 or 21 °0.