A. The simple answer is that most such treatments, if effective, would also kill a lot of the natural fauna. Earthworms, other free-living nematodes, beetles, mites, etc., would die as well, and that’s not desirable.
One treatment remedy has shown promise in this regard, though. Nematode-trapping fungi are free-living soil-dwelling organisms that can effectively kill parasitic larvae in feces. Some of these fungi species have acid-resistant spores that can make it through the intestinal tract of a horse or a ruminant. This means you can feed the spores to animals and ensure they end up in the feces with the parasitic eggs and larvae. But, while there’s been a lot of research done with these fungi over the last 25 years, so far none of these products are commercially available.