Once upon a time when we had those hard core APBT breeders, those men who bred for the ultimate dog with grit and stamina that no other breed of dog could equal. The APBT was the breed of choice for whatever reason and these dogs had to pass the ultimate test to become the breeders of tomorrow.JMO
Think about how many of these dogs got culled...I have heard of people culling five hundred plus in their career. Also, those dogs stamina came more from a conditioning program than just strictly breeding, any dog can be conditioned to reach its potential, some dogs just have more potential than others. Another problem is, with any breed, that not everyone makes them pass the test before they are bred. Or, for pit bulls, another problem is people breeding a dog that had a hard jaw and was a quick finisher, but not necessarily a game dog.
