The normal estrus cycle of dogs is twice a year, usually once in spring from March to May and once in autumn from September to November. When a female dog is in estrus, special signs will occur in her body and behavior. Male dogs have irregular estrus. During the breeding season when female dogs are in concentrated estrus, the testicles enter a functionally active state. When approaching a female dog in estrus, smelling the special odor of the female dog in estrus can arouse excitement and complete mating.

The four stages of canine estrus:

1. Pre-estrus: It is the preparation stage for estrus, which lasts about 7-10 days. The reproductive system begins to prepare for ovulation. The egg is close to maturity, the reproductive tract epithelium begins to proliferate, gland activity begins to intensify, secretions increase, the vulva is congested, the vulva is swollen, flushed, wet and lubricated, and mucus mixed with blood flows. Male dogs often come after smelling it, but female dogs are not allowed to mate.

2. Estrus: It is the period when the signs of estrus are most obvious and mating is accepted, lasting about 6-14 days. The outside continues to swell and soften, the mucus flowing out becomes lighter in color, and the bleeding reduces or stops. The bitch takes the initiative or stops. The female dog takes the initiative to approach the male dog. When the male dog climbs up, she takes the initiative to step down on her waist, face the male dog with her buttocks, tilt her tail to one side, and open and close her vulva to allow mating. 2-3 days after estrus, the female dog begins to ovulate, which is the best time for mating.

3. Late estrus: The swelling of the vulva subsides, gradually returns to normal, the temperament becomes quiet, and male dogs are not allowed to approach. It usually lasts for two months and then enters the anestrus period. If you are pregnant, the period after estrus is the pregnancy period.

4. Anestrus period: the reproductive organs enter an inactive state. It usually lasts about 3 months, and then enters the next proestrus.