A ***** really shouldn't be bred that soon again at minimum there should be a full year from when her last litter left her. It's extremely bad for both the health of the dam as well as the puppies. Most people wait more than the minimum one before breeding again
A commonly held misconception. The uterus ages equally whether or not a ***** become pregnant through a heat cycle, and as another poster said, without a pregnancy the risk of pyometra increases significantly. You may not be aware, but pyometra can be life threatening. As long as the ***** is healthy, there is absolutely no reason she cannot be bred back to back. It may not make sense for other reasons, it's a lot of work, an appropriate stud might not be available, etc., but if she is otherwise healthy, the need to give her a "rest" is a myth born out of our need to anthropomorphize our dogs, and your statement that it is bad for the health of the puppies has no basis in fact whatsoever.