[kavykrazy]

Herding dogs and other working type dogs need to be carefully bred to keep the working instincts intact. Therapy dogs and other helper type dogs can be adopted from shelters if they are carefully screened.

Considering that the majority of shelter dogs are large breed crossbreds(which are harder to place), the problem is mostly caused by careless owners who don't spay and neuter their pets, thereby having lots of "accidental" pregnancies.