Estrus cycle:
* Proestrus: This is the first stage, lasting about 7-9 days. The dog's vulva swells, bloody vaginal discharge appears, and she might be more affectionate and restless.
* Estrus: This is the "fertile" phase, lasting about 5-9 days. The discharge turns clear and watery, the dog will readily accept mating, and she will "stand" to be mounted.
* Diestrus: This is the stage after estrus, lasting about 60-90 days. The discharge stops, the vulva shrinks, and the dog becomes less interested in mating.
* Anestrus: This is the "resting" phase, lasting about 4-5 months. The dog is not receptive to mating and her reproductive organs are inactive.
Key differences from human menstruation:
* No shedding of uterine lining: Unlike humans, dogs do not shed their uterine lining during estrus.
* Hormonal differences: The hormonal changes involved in the estrus cycle are different from those involved in the menstrual cycle.
* No regular cycle: Dogs don't have a regular monthly cycle like humans. The time between estrus cycles can vary depending on breed, age, and other factors.
It's important to note that:
* Not all dogs will show all the signs of estrus, and the length of each stage can vary.
* If your dog is in heat, it's important to keep her away from intact male dogs to prevent unwanted pregnancies.
If you have any questions or concerns about your dog's estrus cycle, it's always best to consult with a veterinarian.