A female dog will have heat cycles for most of her lifespan. As she ages, the fertility drops off, and by 9 or 10 years of age for most breeds, litter size and reproductive efficiency has dropped considerably. Many breeders retire a breeding bitch by the time she is 6 to 8 because of this, and also to give her a break from the cycle of pregnancy and puppy rearing. The heat cycle is draining and an older female does not spring back as quickly from the process. For large and giant breed dogs with a shorter lifespan, reproductive success drops off earlier. Once a bitch’s breeding career is over, a breeder will have her spayed.
If a female dog is not going to be bred, it’s important to have her spayed. If repeated heat cycles occur without a pregnancy, this can lead to abnormalities in her reproductive tract. As the dog ages, she may be more prone to uterus infections (endometritis) which can progress in some cases to pyometra (a pus-filled uterus) and can be life-threatening. Her chances of developing cancer of the mammary glands are also increased if she is not spayed young. Another advantage of spaying the female is that there is not the need for diapers or household clean-up at heat time. The neighborhood male dogs will also stop trying to break through your screen door every time she goes into heat.
Talk to your veterinarian about spaying female dogs that are not intended for breeding. Apart from the health benefits for the dog, spaying all non-breeding dogs is another way to control the unwanted pet population.