It has been and probably will be for some time, impossible to make a vaccine
against worms that parasitize animals. This has been a dream of many people
but it was only recently that I read a paper that even hinted at the
possibility of being able to do this.
One way to safely cut down on deworming is to pick up all the manure every day
and take it away. I have done this for years and each time I (infrequently)
have a fecal done, there is no evidence of worms in the manure- none!
I have a relatively small place but the it may be something to consider doing.
I only worm my guys about 3-4 times a year. If a new horse comes in, they go
into quarantine for about 2 weeks and are wormed immediately.-Amy