Noguchi, Y.; Watanabe, E.

Pseudopregnant recipient females are essential for transplanting early mouse embryos during individualization. Traditionally, pseudopregnancy is induced through mating stimulation with vasectomized males, targeting females in proestrus or estrus. However, group housing of females in animal facilities often leads to fewer females entering estrus due to the Lee-Boot effect. This study focused on utilizing non-estrous females and the Whitten effect to produce pseudopregnant females. Females exhibiting characteristics of non-estrous states were visually selected and paired monogamously with vasectomized males for three consecutive days. This approach resulted in a high copulation success rate of 72.1% (CLEA Japan, Inc.) and 77.0% (Japan SLC, Inc.) on the expected third day. Subsequent embryo transfer using successfully copulated females resulted in offspring from 93.5% of ICR females from CLEA Japan, Inc. and 89.6% of ICR females from Japan SLC, Inc. Additionally, the suitability for embryo transfer could be determined by observing the condition of the ampulla of the oviduct. While this method requires a three-day preparation period compared to conventional approaches, it offers an effective alternative for creating pseudopregnant females for embryo transfer, potentially reducing animal use and associated costs.