Effects of Stimuli Associated With the Male on Litter Size In Mice

Abstract

The oestrous cycle in the mouse lasts about 4 days so that in a population of sexually mature females one expects about one-quarter of them to be on heat every night. When single female laboratory mice that have been reared together with other females are placed with one vigorous male in a clean container, the oestrous cycle is affected in many of them. Oestrous is delayed in some and hastened in others with the result that fewer than expected copulate on the first, second, and fourth day, and more than expected copulate on the third day (Whitten 1956). This phenomenon has been called the Whitten effect (Nalbandov 1964). Whitten's data were records of copulations as judged by presence of vaginal plugs.