Just like humans, dogs do have menstrual cycles, too. Also called the “heat cycle” due to their association with a dog’s fertility period and propensity to have sex, they have some very crucial differences from the cycle that humans do experience.
For the record, dog’s menstrual cycles aren’t really menstrual cycles. This is because their cycle is more of an estrous one. In fact, only primates do have a menstrual cycle. With that said, a dog’s estrous cycle is quite lengthy, with an entire cycle taking about 7 months to complete on the average.
A dog’s heat cycle is composed of 4 stages, with each stage being triggered by the production of certain hormones. The first stage of a dog’s menstrual cycle is called proestrus. Usually lasting for 9 days, this is characterized by a bloody discharge coming out of the vulva. During this period, a dog doesn’t have any interest in mating.
The second stage is the estrus stage. Commonly lasting for 7 days, this is the time wherein the dog is very much willing to mate. Ovulation takes place during this stage, with it typically happening on the second day of estrus. This is the time wherein a dog is “in heat” and most suspect to being pregnant.
The diestrus is the third stage of the cycle. If the dog is pregnant, this is when gestation happens. Diestrus usually last an average of 60 days, and during this period, the dog is not willing to mate, whether she is pregnant or not.
The fourth and final stage of the cycle is called anestrus. Usually lasting up to 5 months, this is a period of “dormancy” for the dog. After this, it goes back to proestrus, and the cycle is going to repeat itself.
Understanding your dog’s menstrual cycle is important if you’re intending to breed dogs, and knowing how this cycle works is going to help you better understand your dog’s behavior.