Do you want to kill the feral dogs or ward them off? Two totally different things that call for two totally different types of dogs that are really opposite from one another. A big lgd will ward them and send them away with probably no injuries being exchanged, a bullbreed is going to break it's neck trying it's hardest to kill them and stop them from getting away, many injuries will be exchanged both ways regardless of how good at fighting it is. It might kill a pack of them but due to the fact it forced the fight it will take injuries from it's desperate victims.

It's only saving grace would be the fact it's probably too slow to catch a feral dog.