A female should not be bred before age 2. They should be retired around age 8 (it depends on the female, some have a harder time so are retired by age 5-6 whereas others are only bred every 2-3 years and may have their last litter at age 8). 4-5 litters should be the limit. If the bitch has a c-section, much fewer would be appropriate.
If a bitch has a small litter and handles it very easily, they can be bred back-to-back (meaning the next heat cycle) and then are rested for a year or so. Otherwise a cycle should be skipped between litters. Many reproduction specialists recommend the back-to-back breedings and younger retirement age if the bitch can handle it.