Breeding ANY animal dogs, cats, horses, cows, etc have a risk associated with breeding. My wife and I have owned Bullies for 6 years and breeding for 5. We have had many litters and each litter is it own challenge. In addition to finding the right stud or bitch, getting the deed done and then the waiting.
Except sometimes mother nature is not cooperating. Females in heat or once bred can develop a problem called PYOMETRA. The results are either full spay in an emergency surgery or risk death. Even the surgery has a chance on death. If the surgery is successful, your female will be a loving pet for the rest of her life.
Sadly I just had this happen last week. She survived and is now recovering nicely but slowly.
Not trying to scare anyone, just providing facts about breeding.