Never breed your dam after six years of age. Some believe that you can keep breeding your dam until she presents problems, but it is taking a risk. Those problems often start after age six. When a dam starts having problems  after six years old it is time to retire her from breeding. Each litter will get worse. Your dam will tell you when her body has had enough with smaller litters, more deformities, miscarriage, and just not getting pregnant.

Think of your dam. If she gives you a litter of puppies at ages one and a half, two, three, four and five, you are blessed.

New evidence says you can breed your dam in back-to-back breeding's. Meaning you could breed her at two and two and a half, then again at three and a half and four, and again at five. After 5 breeding's. This would give you five litters. By then you should have produced a new female to replace the mother.

A dam’s window of fertility seems to be best between one and a half and six years of age.

Sometimes a back-to-back breeding is beneficial to the dam, and it is considered fine if your dam is not skinny, missing hair, and is in good health. Always check with your vet before breeding and have a pre-breeding exam.