Besides all the reasons, very powerful, given before for not breeding dogs, there is one just as serious: a female dog who is not spayed runs a very high risk of developing breast cancer. All vets will tell you that and I have the personal experience. I didn't spay my first Golden, not because I wanted to breed her but because I didn't want her to have surgery thinking that it would be too painful. She died of breast cancer, after surgery and chemo, at the age of nine. That was a long time ago, I learned my lesson. My next two dogs were spayed as soon as it was possible.