Personally I would never leave them to it, bad advice. Especially if You have some sort of Bull cross, You will end up with a dead dog. I breed Bull Terriers for years and kept seven. 5 bitches I could keep in harmony as we had an alpha female. Our foundation bitch, the rest were all Her prodigy. We also had two dogs that rubbed along together for a while. Our older dog Spike tolerated a pup that we ran on to show for about ten months. Then in the blink of an eye no food or toys or even bitches present. Bang they were at it and it took over ten minutes to get them apart. Both to the vets one