There is always a danger to the female if she is bred to a male considerably larger than she is. The size issue is even more important in smaller breeds of dogs because there is not much room for rror. When purchasing your new pup look for parents that are about the same size as your male. That should give you a pretty accurate idea of what her size will be. As for breeding age. No dog should be bred before to years of age. It gives them time to mature before having a litter of their own to care for.
I hope this helps. Please let me know if you need further info.
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