Several years ago I decided to purge my lines of girls who either could not get pregnant, did not free whelp, or were just terrible mothers. I am getting too old for all that drama! I find the use of herbs and "feed to breed" interesting and got this e-mail today and it has some interesting points in it, enjoy.
http://www.revivalanimal.com/articles/managing-females-for-reproductive-health.html?a=rev120622p

Interesting, but a bit of an over simplification. What about the bitch that conceives 12 puppies every time, runs out of gas and needs c-sections. What about the bitch that has a 2 puppy litter, followed by litters of 7 and 8 puppies. Things are never simple and cut and dried.