Veterinarians and reputable breeders recommend waiting until a female dog is at least 1 to 2 years old and fully matured before breeding her. Male dogs can produce sperm by 6 or 7 months of age, but do not have optimal sperm quality until about 18 months old.
Although both male and female dogs can reach puberty by the age of 6 months, early breeding can cause both physical problems and negative behaviors. Also, waiting until a dog is mature allows a breeder to screen the animal for problems such as hip dysplasia, which may not be apparent before maturity. The American Kennel Club refuses to register puppies born from a female less than 8 months old or sired by a male less than 7 months old.