Are you running everything together? If so that is not ideal for feeding? You can't feed them less to make them root more. Also they wont clear three acres without you enclosing them in smaller areas then giving them more as they clear a patch. Wild pigs supplement their diet by rooting for worms, insects, roots etc but would also eat meat by cleaning up dead animals so balance their diet. You can't replicate that.
If you don't feed them enough then they are more likely to knock you over when you go in with the feed you are giving them, than root faster or deeper.
They will not graze bracken back and there is s risk of bracken poisoning. Pigs going to slaughter should be removed from bracken areas 15 days before slaughter according to AHVLA.
What are your long term plans for these pigs?