There are a few things that can cause a miscarriage ... bacterial infection, including "brucelose"... i believe that is the name... if the male is infected with this can cause the litter to miscarry ... also there are other factors that the breeder may have no control like viral infections ... and of course bad nutrition, over breeding, abuse, ...
No matter what any vet i ever had always recommended to wait at least one heat cycle in between breeding's... meaning that no dog should be bred more than once a year.... most breeders i know also say the same... and even on the internet there is a lot of recommendations about waiting in between whelping s to make sure mom has time to recover well.... so she can give the best nourishment for the next litter...
Good Luck in your next family addition !!
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