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Originally Posted by Skratikans
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someone is insisting that when a female dog comes into heat...she has a period (blood and the works)....is this true?
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Actually, this is not true. In humans, the "period" is the sloughing off of the lining of the uterus.
In dogs, the little bit of bleeding we see is part of the "estrus", or
heat cycle.
The first thing you notice about a female dog (profanity filters won't let me say *****) going into heat is a swelling of the vulva, some bloody discharge and a lot of interest from neighborhood dogs. This is called the Proestrus or "follicular stage", and the ovarian follicles are increasing in size and changing shape. A female won't be interested in breeding at this point, because she still hasn't released her eggs. This will last between one and two weeks, depending on many factors.
The next stage is the actual Estrus. You can tell when this has started, as she will be receptive to breeding. If you were checking her blood, you'd notice that progesterone levels had suddenly shot up, triggering ovulation. Many breeders use progesterone levels to approximate the very best time for breeding. This lasts for another week or so, depending on several variables like the body weight of the dog.
At no point will a dog (or most animals for that matter) have a "period" that is analogous to that of humans and other large primates.
It's possible that because, in nature, these animals virtually always become pregnant after every heat cycle, that the actual pregnancy/birth cycle is intended to clean out the lining of the uterus as the menstrual cycle does in primates. No one knows for sure.
bob