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This type of embryonic diapause (facultative) is the result of a previous litter being recently born and the consequential pups suckling during lactation that promotes prolactin to be released, which in turn reduces progesterone secretion from the corpus luteum in a pregnant female. The corpus luteum is a temporary endocrine organ that is formed from the leftover cells from the ovarian follicle in the ovary, once it has released a mature ovum. The main function of the corpus luteum is to secrete progesterone during pregnancy in order to maintain the uterine environment needed. Prolactin acting on the corpus luteum causes the progesterone level to be below optimal concentration and therefore induces embryonic facultative diapause. When there are shortened daylight hours, meaning lower temperatures, melatonin levels are increased which enhances prolactin secretion and also enables facultative diapause. Both of these scenarios happening together is common, and the marker of this type of diapause, with the outcome being to ensure the embryo currently developing into a fetus has the highest chance possible of survival after birth.

Each species that undergoes facultative diapause tends to have a specific developmental stage, that is genetically determined, in which this process is initiated. It is seen as a plastic response made up of an alternative developmental pathway programmed by the stimuli previously mentioned.

Most studies are done on rodents and therefore we are still unsure whether the model we have for the mechanism of facultative embryonic diapause is sustained across all species of mammals.