Just being Mean

I'm pretty sure this is a dominace thing, but i wanted to be sure.

I have 7 girl piggies together. Most of them leave each other alone, but the biggest one, Peep, is just plain mean to everyone.

Sometimes I can hear one of them squeaking over and over because Peep is biting their ears or fur or skin, but the pig being bitten doesn't move or retaliate, the just cry out in pain.

Is there some way to discourage this kind of behavior?

-Dan III