1. Proestrus - This stage, unlike humans, begins with the appearance of vaginal bleeding / blood. Beware of your dog staining furniture etc.
From the very start of the bleeding is DAY 1. It generally lasts from 4 - 9 days. Male dogs become very interested in the female; however, she will not yet mate with them, as her body is not ready to conceive. She will be a bit more nervous than usual. Her vaginal area will seem more puffy and reddened. For young dogs note this first date and subsequent dates to obtain any pattern.
2. Estrus / Oestrus - Ovulation begins. This is the stage in which the female will accept the male and conception can occur. The vaginal discharge is much less and more yellowish than bloody. Ordinarily, the stage lasts for 4 to 13 days. Your female will generally stand still, appear servile, and hold her tail to the side when you touch her back, or a male dog tries to mount her. This can start around DAY 5.
3. and 4. Metestrus and Anestrus - Diestrus- These 2 stages are periods of ovarian activity, but with no significant outward signs. This basically means, out of heat, but there could still be things going on inside. False pregnancies frequently occur during Metestrus. From DAY 1, your dog may still be going through her cycle until around DAY 21.
5. Dormus - This stage is the remainder of the six-month-cycle, where the bitch appears normal, about 160 days.