You have definitely come to the right place to find information.....you have already received a lot of it in the few responses you have received. I too am an aspiring breeder and have been so fortunate in finding very knowledgable breeders to teach me all that I can cram into this head of mine.
Like mentioned above, breeding puppies from pet stores is not a good idea. If you are truly interested in breeding to better the breed (which should be your main goal in breeding), I would recommend that you have your current babies fixed and keep them as pets. Spend some time looking into all of the aspects of breeding and start learning as much as you can. There are some exceptional breeders on Yorkie Talk who are always ready to help those of us who are ready to learn. I definitely recommend finding a breeding mentor.......I haven't even begun to breed and yet I don't know what I would do without mine! After doing all of this, if you still have the desire to breed these beautiful little dogs, then purchase some breeding quality Yorkies to get started.
Good luck!
__________________  Jen and the Bloomin' Biewers Gang |