A bitch generally has her first estrus season, or heat, at between 6 and 12 months of age, most commonly between 8 and 10 months. Mating will produce a litter at this age, but she is immature, so it is important to guard against that potential. A female dog will normally return to season about every six months. Some have estrus seasons as often as every four months or less. If you are not a serious breeder, the healthiest thing you can do for your female puppy is to spay her before she reaches sexual maturity, according to the PetMD website.