The female breeding dog poses several problems to their owners when they are not being bred but kept open for their first few heat cycles, which is the dogs version of a menstrual cycle. A reputable breeder will wait until the female dog is fully grown before breeding her. That means waiting until she is 2+ years old. By that time she would have gone through at least 3 heat cycles.
Besides keeping the female away from male dogs for her 3 week heat cycle every 6 months the owner should also keep the dog in good health during those cycles. That means the dog should be getting iron supplements and vitamins for menstration. Iron will be the most common supplement the dog will need but fresh organ meats like liver would provide that. Often adding dry puppy food to the dogs diet will provide many of the needed vitamins.
Another problem is the blood that the dog oozes. Most of the time the dog will keep herself very clean but the larger breeds of dogs can drip blood all over the place. The dog owner can either purchase doggy diapers for the dog or have a kennel ready for her, preferably an indoor kennel where she can be kept away from male dogs.
The odor that the female dog emits will be strong to male dogs. They seem to know where a female is, even if she is miles away. That is one of the main reasons you will want to keep the female dog inside during her heat cycle is so she will not be the dog magnet of the neighborhood.