I do think the key is in identifying what worms your flock has, then treating with a the correct wormer. best way to do this is with routine fecals, which you can have a vet do, or you could do them yourself if you're willing to invest in a scope, centrifuge, and misc supplies.
This peafowl...
It almost sounds like you're saying that worms don't kill chickens, or maybe I'm missing something?, cause I have seen the irreversible damage in picture and in my own necropsies, and I can assure you that cause of death was from an infestation of worms.
-Kathy
In the UK
Panacur AquaSol 200 mg/ml oral suspension for use in drinking water for pigs and chickens
Species:Pigs, Chickens
Therapeutic indication:Pharmaceuticals: Endoparasiticides: Anthelmintics for pigs, Anthelmintics for poultry
Active ingredient:Fenbendazole
Product:Panacur AquaSol
200...
There is only one FDA approved wormer for laying hens, it's hygromycin B, which is what's in "Booster Wormer Triple Action". Wazine is approved for meat birds, as is fenbendazole at a very low dose.
There are plenty of other drugs that can be used "off label", but don't confuse "off label"...