Each year, so-called "Class B" dealers provide some 42,000 dogs to laboratory and veterinary research, their nurturing and treatment prior to sale regulated by the federal Department of Agriculture. But the kennels are many, and the inspectors limited in number. Abuse, according to the documentary "Dealing Dogs" (9 p.m. Tuesday, HBO), is widespread, sometimes involving kennel operators who not only mistreat the animals, but obtain their stock from pet thieves.