Spaying your female dog
The question is rather when is the best time to spay your dog? According to the above mentioned article and most veterinarians, the answer is before sexual maturity. It is easy to admit that if your dog is spayed before her first heat cycle (usually 6 months of age), the chances of accidental pregnancy and unwanted litters are zero, which is great, because the problem of overpopulation shouldn't be ignored by any responsible pet owner. So the simple answer may seem to be: the sooner the better.
However, unfortunately there is no simple answer. As this publication explains, not denying the overall advantages of spaying, new research shows that female dogs spayed before the age of 6 months are more likely to suffer hormone-related urinary incontinence. Similarly, male dogs neutered at an early age are more likely to suffer from certain diseases than those neutered later on.
It still gets more complicated though, as sterilization (disabling your dog from reproduction) does not necessarily equal spaying (or neutering in male dogs). In modern veterinary practice, it is possible to sterilize your female dog without actually removing the organs responsible for producing the sexual hormones as you'll find out from this article.
How are you then, the pet owner, to be expected to make an educated decision about spaying your female dog if there doesn't seem to be a consensus among veterinarians on the issue?
If your number one reason for spaying your dog is avoiding unwanted pregnancy, then you should definitely get it done before the first heat cycle. Otherwise, consult with your vet and see if new research has come up with more evidence on the matter.