You can talk about many things:

The number of healthy dogs put to sleep every year because of shelter overcrowding

The fact that shelters often have purebred dogs

The fact that most dogs end up there not because the dogs are a problem (common misconception) but that people have a problem

The fact that shelter dogs are often pre-trained, and you can get a trained dog who is past its teething stage, but is still young and has plenty of life in them

Is that enough?