OK.
As a last resort if they wont go in for food....
Feed them at the bottom of the ramp...get a large bucket or small dustbin (black if you can) and stick it over their head (obviously one at a time) Hold on tight and the pig will try to reverse. Stand over the pig, a leg at each side and try to reverse it up the ramp, if needs be steer the back end with the tail. Have food in the trailer to occupy the ones you get in - and someone to help ensure they dont get out again.
Used this only 3 days ago trying to get a friends 3 sows into the trailer.
Oh yea - don't forget to curse a lot at the same time.
Good Luck