Production of timed pregnant mice by utilization of the Whitten effect and a simple cage system

Pregnant female mice with an impregnation time of 4 hours were achieved by utilizing the Whitten effect and a simple caging system. The cage consisted of a mobile wire-lattice which divided a plastic cage into two compartments to separate the females from the male but still allowed some contact. A synchronization time of 72 hours succeeded in an average copulation rate of 28.1 +/- 5.39% when the procedure was conducted in the forenoon.