Female dogs typically stay in heat for about 2 to 4 weeks, with the average duration being around 18 days. This heat cycle, also called estrus, has distinct phases:
- Proestrus: Lasts about 7 to 10 days. The vulva swells and bleeding begins. The female attracts males but is not receptive to mating yet.
- Estrus: The mating period lasts about 5 to 10 days. Bleeding decreases or stops, and the female is receptive and fertile.
- Diestrus: Lasts from 10 to 140 days after estrus, during which the female is either pregnant or resting.
- Anestrus: The resting phase before the next cycle, lasting about 4 to 6 months
In summary, the "in heat" period when a female dog is fertile and receptive to mating is roughly 14 to 21 days, with some variation depending on breed, age, and individual factors. Most dogs go into heat about twice a year, every six months on average
