Originally posted by Complaintdesk:

Once your 2 star boar is tamed, tame another regular boar, preferably in the same enclosed area. Once tamed they will breed and the offspring of the 2 star will always be another 2 star boar.

I strongly recommend taming 2 animals at the same time. It's quite the time sink, so repeating it as little as possible is preferable. One thing you can do while waiting for the taming to finish is grind some stealth skill.