All unspayed female dogs go through puberty and experience heat, or estrous, cycles. When puberty starts for female dogs depends on factors such as your dog's diet, size and breed. Understanding her heat cycles is important to keep her healthy and safe.
Dogs' Heat Cycles
After reaching puberty, dogs typically experience two heat cycles each year, or one every six months. Each cycle lasts about two or three weeks. Heat cycles are comprised of four stages: anestrus, proestrus, estrus and diestrus.
Proestrus is the second stage of heat. This stage lasts nine days on average, although it could be as short as three days or as long as 17 days. During this stage, males become interested in mating with females, but females are not yet interested in males. Throughout the proestrus stage, the vulva swells and bloody discharge is expelled from the vagina in varying amounts. Female dogs' estrogen levels peak at this stage, before suddenly declining during the estrus stage.