This plug may fall out after 24 hours. Visualization of this plug in the vagina or in the cage can be used as an indication that mating has occurred. The actual mating may not be observed as it often occurs at night. Ovulation occurs 8-12 hours after the onset of estrus. Therefore, depending on when mating occurs, fertilization of the egg may occur at almost any time within the 24 hours of estrus.
Fertilization occurs in the proximal oviduct ampulla.
Implantation may not occur until day 5. Implantation can be delayed even longer if the dam is lactating heavily. Delayed implantation does not occur in the rat. Physical stimulation of the cervix and vagina is necessary for luteal development and maintenance of pregnancy. This is important if artificial insemination is performed.