I've never wormed my pigs and each time they are butchered the inspector says he's never seen such nice clean livers.
Of course mine are on pasture and they have a really big area. Plus I clean the area everyday and use plenty of barn lime on all areas where feces was removed.
Each year we rotate pastures so this years pigs are not on last years pastures.
This years go to the processor the last week of Oct, they started out as 22# piglets on June 1 and as of yesterdays measurements they are all at or slightly over 300# each!
I've been raising hogs for 24 yrs now plus my dad -a long time hog farmer never wormed either. Good pasture & housing management wiil work but it is very time consuming.
For those who don't want chemical wormers you can mix Diatomaceous Earth in with their grain.