Proestrus

Proestrus comes after, obviously, the previous one which we normally know as "heat", when the vulva swells up and starts a bloody flow, moment in which the female is very attractive for the males, although she still refuses them and can not, at this stage, become pregnant. At the end of this stage, the levels of estradiol reach their peak, preparing the uterus for a possible pregnancy, meanwhile the vagina and cilia of the oviducts suffer important changes in order to be ready for the upcoming events in the estrus stage.

On average, the proestrus stage lasts approximately 9 days, although there are cases of it lasting between 2 to 30 days in some females. Curiously and although physiologically all female dogs suffer the same hormonal changes during estrus, these do not necessarily show up in the same way in all of them, varying in intensity and duration. In some cases there can't even be the so-called "white heat" or "silent heat" in which there is no hemorrhage and even sometimes the bullet is not increased excessively in size and therefore goes unnoticed to the owners, unless they happen to have a male at home, who will undoubtedlt be after her … at all time! In the moment that the female is receptive, the proestrus stage ends, giving way to the following one.