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Successful mating in rats and mice is verified by the presence of a vaginal plug in the females. The vaginal plug is formed from the mixing of vesicular and coagulating gland secretions at the time of ejaculation. Vaginal plugs may be retained in mice for 16 to 48 hours, but often fall out of rats within hours after breeding. Direct observation of the vaginal plug in the vagina or its presence in the waste pan beneath suspended wire caging is a good indication that mating took place. Another technique utilized to detect mating is vaginal lavage and microscopic examination for the presence of sperm. Presence of the plug does not guarantee that an animal is pregnant, thus mated animals should be observed and later palpated to confirm pregnancy.