A small side note: shaggy mane (Coprinus comatus) has also been shown to kill - and eat - nematodes. No idea how efficient it is, or if it attacks the species that are problematic for sheep, but I thought it was interesting. Also, since it's mostly a saprotrophic fungus, and grows in meadows and lawns, it shouldn't be all that hard to introduce it to a pasture where there's a nematode problem. Might be worth a shot.
A nice video about shaggy mane and other inky caps:
And
here is the study he's referring to.
(Edit: It might not be the exact one, they mention an earlier study about this, but it's an interesting one anyway.)