It sounds like you did everything you can.
With all due respect, I don't understand all this talk about dogos maturing slower than others, that's bull. Those aren't dogos, the dogo should be crazy to catch good sized shoats by 4 or 5 months and able to catch something twice its size by 6 or 7 months.
Throw a hog head in with a bunch of puppies and they should rip it up, let them play with a shoat and they will kill it. You can tell very young if they are dogos are not.
How many dogos have you seen that are the way you describe?