sadly, the great majority of dogs in the US are born to people who want their dog to have "just one litter" or that think their dog NEEDS to experience motherhood to be whole. In reality, it's NOT natural for members of the canine world to have babies. Only the dominant female will breed, the other females all act as caring aunts and help raise the babies.
I just get so sad because I see it every day and I'm not even involved in any kind of dog rescue. My co-worker is on her EIGHTH!! dog in the 5 years I've worked there. She gets cute little puppies that people have bred (usually for just one litter!) and keeps them a couple months and gets bored with them. Then they either get shuffled from home to home (they are horrible biters and not housebroken because she never does any training) or she just starts letting them roam and they get hit by a car. One died of Parvo while she was at work. She knew that the pup was sick and that it had parvo. But geeze, it was just a dog - she'd get another one if that one didn't make it. It suffered all night long, left out on her back deck. At lunch, she went home and it was dead.
She then complained every time she brought in another dog that she had to pay $7 to buy a vaccine from the feed store because "that dog brought parvo into her yard".
Any time anyone has a litter of puppies, she is always the first person to step and say that she'll take one. Of course, the people who bred the pups don't care one way or another once the pups are gone. She had gotten at least 2 pups from the same person. The second pup was FREE!! because the breeder felt sorry that the first pup had died. Yeah, I'm sure that she didn't tell her that the pup died because she decided it was too much work to put the pup on his tie-out so left it to run free and it was hit by a car. Just like 4 dogs she owned before that one.