I first want to say some back yard breeders are more resposible than big time show breeders 2 examlpes. My dad only bred when our waiting list was over what we knew our girls could produce and we knew our puppy parents would be.(freinds and relitives) None of our dogs in 15years ended in a shelter (we found a new home for the 1 pup we ever had to have returned Cancer intered the owner had to go to a nursing home a single guy. I ended up keepinng the dog and showing it. Pretty good record for 25 pups all but 2 were fixed by 1 year old no other litters. The 2 unfixed were ones we kept.
The second example is Merlins breeder. She had a list before breeding her dog always had small litters 5-6 pups . Bred to the same male (she was the only female they mated him with)so no sexual diseases. Before breeding K would beef up calcium and vitamins to the female( Neslie) Then after pups and when they were eating they got supplemnted too. She did not wean until Neslie did or at 10 weeks. She didn't do shots but she went above what I had for standards for what I was looking for (thats why it took 4 years to get a puppy for me LOOOONNNGGG wait) Of course after that wait I choose the only one she has ever had with a medical Problem.(he has an irregular heart beat). Wich made K think it was time to retire Nestlie so she and Merlins dad (owned by someone else) were both fixed. I don't know if she kept any one to replace her but I doubt it.
Most breeders I have know (when I was activly showing ) also ran a passive rescues (they whould get calls for help finding homes for their breed)all would take back thier own dogs in a flash.