My stock boar developed meningitis shortly after he arrived,he was only 5 months old i think the journey braught it on he was braught up from dorset.This weather can bring it on as well sudden change from cold to heat happens a lot in commercial pigs. Anyway i managed to save him and he has sired many piglets. I gave him the appropriate doses for his size of pen and strep in one side of his neck and lincocin an anti-inflammatory in the other side for thee days but he was down and wouldnt get up Importantly you must get as much water into him as possible i use an old plastic juice bottle and try to get it into the corner of his mouth and massage his throat to induce the swallowing affect,you waste a lot but he will get some, It wasnt a one off i save a few commercial pigs this way when we had them.
Good luck i hope he recovers
Arl