Hi Mary-Ann, I concur with what Libby had to say, if the bitch is in good health and maternal duties come easy to her then six litters would not be excessive. For myself I have yet to breed more than three litters from any one bitch that I have owned, two bitches were bred for a fourth time but in both instances they were empty. I don't breed my bitches before the age of two and some have been into their fourth year before a first breeding. Some decisions are governed by whether or not the economics are justified and if that sounds cash driven I would point out that I see no point in re-breeding a bitch who lacks sufficient fertility to justify the expense of a stud fee coupled with elective C-Section. I have had good producing bitches who may have had to be sectioned and there is a limit as to how often I will do that.
I don't know that repetitive pregnancies are any more a health hazard for some bitches than a single pregnancy might be for another. Rose T.