Female dogs that aren’t spayed go into season or into heat approximately every 6 months. This can be a real annoyance to pet owners and to all other pets in the household.
The heat cycle for a female dog lasts about 3 weeks. During that time her vulva will swell and she will have a bloody discharge. While she is in heat your dog will be constantly releasing pheromones which will attract all the male dogs in your neighborhood.
Do not leave your female dog alone outdoors when she is in heat. Male dogs will become aggressive and have been known to dig and jump fences to mate. Keeping your female indoors will help eliminate the fear of unwanted puppies or attacks by neighborhood males.