Cycle of female dogs

With entrance of the sexually maturity, the so- called “heat” begins for the first time. This varies from dog to dog and also from breed to breed, but in most cases starts between 6 and 12 months. Smaller dog-races become sexually mature earlier, bigger breeds usually in the second year of life. The reason for this is that the female dog must reach a full body weight, otherwise pregnancy cannot function anatomically. On average, female dogs will heat once every 7 months, although this may vary from individual and breed. The first heat can also take place in silence, which means that there no external signs, such as bleeding, but hormonal changes in the blood can be detected. It can also come to a so-called split-oestrus, with which first signs are to be determined externally, but these disappear after a few days again. How a typical cycle works, is explained in the following.

The four phases of the cycle

Proestrus

The so-called proestrus, is the first phase of the heat and lasts on average 9 days and varies in the duration between 3 and 17 days. In this section, the vulva (vagina) swells and there is a bloody discharge from the vulva, with the amount of blood varying from dog to dog. It can also happen that the female dog hardly loses any blood. It is important to note that the dog is not fertile at this stage of the cycle, although care should be taken at this stage as well, as the individual stages are often seamless. However, they do have a very tempting scent for males. In this phase the females shows an uninterested behavior in pairing, she avoids the amorous approach attempts of the males and shows also quite clearly her disinterest in a copulation.

Heat

In the actual heat, the oestrus, the female dog is fertile and ready to mate, she lasts on average 9 days and varies in the duration 3 to 21 days. In this phase she has several ovulations, usually between the 2nd and 4th day. You can call this section also “standing heat”, since she shows an own behavior in these days. When a dog, ready to mate approaches her, she stops and turns her tail to the side. The vulva is no longer so strongly swollen and the discharge is no longer bloody, but watery to slimy. 

Metestrus

In the metestrus most symptoms of a heat subside, the vulva swells completely and the vaginal discharge becomes yellowish until it disappears completely. From the outside, the female dog does not show signs anymore, but the she is subject to a hormonal change. Regardless of whether she has become pregnant or not, the corpus luteum in the ovaries produces the hormone progesterone. The degradation of these corpus luteum hormones can take up to 12 weeks (luteolysis). The sinking progesterone level can now lead to an increased release of the hormone prolactin, which boosts the milk production of the female dog. This can have the consequence that it can come with some females to a false pregnancy

Anestrus

The last phase is called the resting phase (anestrus), in which the female dog no longer shows any signs of heat and can vary in length from dog to dog (weeks to months). In the transition phase from resting phase to proöstrus, follicles form in the ovaries, from which the oocytes later grow.