Get the best boar you can (ideally 1 or 2 stars) let it aggro you and follow you back inside of some preconceived enclosure of your choosing, give it food (throw a stack of berries or carrots in) and hang out close by where it can't see you. Wait until it becomes tame ( you can check tame level by hovering mouse over boar) . Keep fire of any kind at a good distance from the enclosure. Go get another boar.

If any boar mates with a 2 star boar their is a 50/50 chance the offspring will be a 2 star.

To get them to mate wait until they are hungry and throw a stack so they eat at the same time

pet them.

the big secret is that the "breeders" are completely unnecessary, just wait until they are all hungry and throw a stack , they will breed.