Since we've had a problem with one of our cats having tapeworms, I asked the vet if I also needed to worm our older puppy for tapeworms too since he always seems to have his nose up her butt.
The vet said no, they get the tapeworms from fleas; not thru the feces.
I worm my chickens once a year, with whatever broad spectrum wormer I have handy. I have neighbor that raises cattle and he gives me the wormer in small amounts so I don't have to buy a huge bottle for just 14 chickens.
Year one I used valbazen (albendazole), 1/2 cc. orally, undiluted for standard sized chickens; 1/4 cc for bantams.
This year I used ivermectin, 1/2 cc applied to the back of the neck, on the skin.
Withdrawel time for either is 2 weeks.
IMO, DE - wormguard, worm-x, and all those other natural products are more preventative than treatments.
I feel that worming once a year is a good idea because once you notice a problem weight loss, worms in the stools, the infestation is bad and the damage is already done.