Welcome to YT! Lots of good advice so far.
4 lbs is not a safe recommended breeding weight for a female. The general rule of thumb is not to breed a female under 5 lbs, and even then there are other factors (like pelvic structure, size of the other dogs in the line, etc) to take into consideration. Being as your girl is 1 yo now, it's not likely that she will be big enough to safetly breed.
If you desire to breed in the future, I suggest that you find an experienced breeder to mentor you while you are learning. All the research in the world is no substitute for the first hand experience you would get from working with a mentor. |