A protocol for rat in vitro fertilization during conventional laboratory working hours

In vitro fertilization (IVF) is a valuable technique for the propagation of experimental animals. IVF has typically been used in mice to rapidly expand breeding colonies and create large numbers of embryos. However, applications of IVF in rat breeding experiments have stalled due to the inconvenient laboratory work schedules imposed by current IVF protocols for this species. Here, we developed a new rat IVF protocol that consists of experimental steps performed during common laboratory working hours. Our protocol can be completed within 12 h by shortening the period of sperm capacitation from 5 to 1 h and the fertilization time from 10 to 8 h in human tubal fluid (HTF) medium. This new protocol generated an excellent birth rate and was applicable not only to closed colony rat strains, such as Wistar, Long-Evans, and Sprague-Dawley (SD), but also to the inbred Lewis strain. Moreover, Wistar and Long-Evans embryos prepared by this protocol were successfully frozen by vitrification and later successfully thawed and resuscitated. This protocol is practical and can be easily adopted by laboratory workers.