Wormwort grows wild right by our wooded parcels, and it's a huge part of our worming regimen.
When I was talking with a prospective processor the other day, he shared with me than one of his old timer customers never processes his hogs until after the fall pumpkin season. Cleans them out beautifully every time. And if you ever have occasion to feed whole pumpkins to chickens, watch what they eat first: it's the pumpkin seeds. Then the strings, then the rind. The worming power is in those seeds; if you can get a good supply of raw pumpkin seeds year round, you can add that to your ration when you need to. Rotational grazing is also good for them, too, so the parasite load doesn't get to be too much.