So...
I'm not in a great mood, will try not to be deliberately insulting. There's an old adage, "the dosage is the poison", and for parasite control, parasite elimination, and even for control of bacteria etc that adage holds generally true.
In practical terms, it means that the compounds effective in wormwood, pumpkin seeds, mustard (another high sulphur compound family of plants), etc have to be present in sufficient quantity to do any good (together with the great mass of everything else that makes up the wormwood, garlic, etc that doesn't have the desired bug control properties). But in too high a dosage, they risk doing great harm to your animals. Or yourself.
Naturally grown plant materials have useful compounds, yes - but how much, and in what part of the plant, will vary with species, with planting location, with time of year, and even from year to year. Its what separates herbalism from pharmacy - known compounds in known concentrations offered in known dosages with a generally well known (or at least broadly accepted theory) of HOW, chemically, it does what it is purported to do.
Whenever I am deliberately adding something to the diet with the idea of killing, controlling, or otherwise managing a "problem", I prefer to be deliberate in the dosage. That may not matter to you - but understand that one of us is managing risk with the benefit of hundreds of years of human experience, and the other is little better that sitting in a cave by the fireside telling stories and crushing plants while invoking the Spirit world.
