Why Can’t You Kill Equine Internal Parasites in the Field?

Q. Why isn’t there a worm-killing treatment for the fields? I rotate my horses from one grazing pasture to another and would be interested in some type of treatment after I rotate them off the field.

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.