Protocol for Providing Additional Pseudo-Pregnant Recipient Mice for Embryo Transfer and Intra-Uterine Insemination by Plugging in the Middle of the Day

Abstract

The fact that 10% of female mice enter oestrus and allow mating in the middle of the day is an old  observation that has been more or less forgotten. We here show that this old knowledge can be used to  improve the efficacy of both embryo transfer and insemination protocols. The present technical paper  shows that rapid re-arrangements of mating cages, to achieve pseudo-pregnant recipients in the middle of  the day, can be of great advantage in emergency situations. Such emergency situations occur repeatedly,  i.e. when a scientist has forgotten to re-arrange her/his mating cages, and the last important male suddenly  has become ill and may die within a few hours. A rapid technique for uterine artificial insemination in mice  in such situations is extremely valuable. An artificial intra-uterine insemination requires only a minimum  of planning, a minimum of instrumentation and a minimum of surgical training. The artificial insemination  must be performed shortly after mating due to rapid constriction of the utero-tubual junction (UTJ). This  means that the timing of the insemination is very important. We here show that the success rate for embryo  transfers, when using recipients plugged in the middle of the day, was the same as for ordinary overnight  mating protocols. In addition, it should be noted that the success rate (frequency of pregnancies) for uterine  inseminations was 55% if using F1 recipients of C57BL/6J (considerable lower if using recipients of inbred  C57BL/6J), which is amazingly high, since inseminations in mice is known to be tricky to perform in a  reproducible manner.