Once I explained that all unsprayed female dogs go through this at least once, usually twice a year, they then wanted to know how long they were going to have to put up with the mess and the neighborhood Romeos. The average estrus cycle in a dog is approximately twenty-one days and this cycle usually occurs every six to seven months. The first cycle will often depend on the size of the dog. Small breeds such, as Chihuahuas or Toy Poodles will come into heat between five and seven months. Large breeds like the Collie, Mastiff or Great Dane may have their first heat cycle at six months but it isn t unusual for them to delay until they are a twelve to sixteen months.
Larger dogs develop at a much slower rate than small dogs.
There are three distinct stages of the heat cycle. The first one is the Proestrus and it is during this stage the owner will often notice the bleeding from the vulva. For those owners who keep their dogs in the house, many pet stores carry dog panties that hold special canine sanitary napkins to eliminate the mess. In addition to bleeding, the vulva will also swell and the dog will usually have an increase in urination. The most obvious sign to most owners are the increase in population of male dogs around their house.