The proestrus of a female dog lasts from 6 to 15 days, from the discovery of bloody discharge in the vagina to the time when the female dog is willing to accept mating. Generally, the duration is slightly longer for primiparous female dogs and slightly shorter for multiparous female dogs. During this period, the development of follicles is not very large on animal B-ultrasound. The obvious characteristics of proestrus are swelling and enlargement of the vulva, and the base of the vulva feels hard when touched, commonly known as "hard root". The bloody discharge from the vagina starts out bright red, gradually becomes thinner and dark red. At this time, the female dog often shows a decrease in appetite, excitement and restlessness, and is willing to play with male dogs. The urine and vaginal odor can attract male dogs, but they do not accept mating. Follicles can be seen using animal B-ultrasound observation. The estrus period lasts about 6 to 10 days, from the beginning of willingness to accept male dogs to the period of refusal to mate. During this period, although the vulva is swollen, it has begun to soften and has a tendency to subside. The blood in the vaginal discharge becomes lighter and light brown. The female dog is extremely excited, likes to approach the male dog and has teasing behavior towards the male dog. When the male dog mounts her, she stands still and allows mating. During this period, the follicles mature on animal B-ultrasound. Female dogs usually start ovulating 2-3 days after entering the estrus period, which is the best time for mating.

The late estrus period starts when the female dog refuses to mate with the male dog. If it is a female dog that has not mated or is not pregnant after mating, it usually lasts for about 2 months; if it is a pregnant female dog, it lasts until the end of the lactation period, about 3 and a half months. This period is the recovery stage of the reproductive system. The swelling of the vulva subsides, and animal B-ultrasound observation shows that the corpus luteum is formed in the ovary. The female dog's sexual desire decreases and she is unwilling to approach the male dog.

The anestrus period starts from the day when the female dog is weaned or the end of the late estrus period of non-pregnant dogs to the beginning of the next estrus period, with an interval of about 90-150 days. At this time, there is no abnormal change in the behavior of the female dog. Animal B-ultrasound observation shows that the follicles in the body develop slowly, and the entire reproductive system is in a relatively static state.