Gail Damerow in her book "The Chicken Health Handbook" suggests not to give a wormer unless the chicken is looking rough and poorly. Basically she states that the worms and the chickens have to create an equilibrium between them and that stress or sickness is usually what tips the scales in favor of the worms. It appears to me that she leans to the "don't worm unless needed" mentality.
Something else she states is that worms will eventually get resistant to certain drugs which makes sense to me. So I wonder if routine worming is actually helping the worms get resistant to the drug. She does caution against switching wormers to quickly because in doing so you might actually be letting the worms get resistant to yet another wormer.
Damerow states a one week withdrawal period for *approved* wormers. She states that non-approved wormers (wormers intended for other animals, etc.,) should NOT be used on chickens and that if they are used for chickens that those chickens should not be used for meat or eggs.
Here is a list of wormers she has listed in a sidebar in her book. The book also gives descriptions and specifics:
Coumaphos (Meldane)
Piperazine
Phenothiazine
Levamisole
Thiabendazole
Mebendazole
Iveremctive
Since I've shared some of her information here I guess I need to put a plug in for her book, The Chicken Health Handbook, published by Storey. Excellent book and highly recommended.
As for ACV...hmm, maybe it doesn't really kill the worms but gives the chickens a bit of a "kick" like "joggin in the jug" and helps give them the edge over the worms.
Ed