again worming issues can be very contentious. and there are so many factors to consider, for a start the size of flock and ammount of ground they have is a important factor, for example 20 hens in a small coop with a small run would seems to be a likely candidate for worms, but for argument sake those 20 birds came from eggs you hatched and the run is now so scrated that slugs and snails rarely venture on to it then the chances your birds have high levels of parasites are lowish, however add a bird with a high population of worms in it to the flock and you get a masive increase in the chances of all birds having worms. then there is the free range situation of say 3 hens roaming 1/3 acre all day unhindered. the chances of contact with parasites are very very high however that dosnt mean a high intestinal population worms, as those birds may well have access to natural plant feeds that help purge the worms.
so whats the answer??? well thats an easy one. do what most chicken keepers already do..........watch your birds get to know them well and there behaviour, occasionly look at the odd poo and see if there are worms in it. if you do find worms in the poo and the birds appear totaly normal and are laying well (for layers) then do nothing, if they arnt being normal and you suspect worms treat them, very simple. we do use wormer here but we have thousands of birds although most (except breeding stock,growers and chicks) free range over a very large area, so we pick and choose those we worm, for example if we are going to pen a smallish floch for a couple of months to breed from we tend to worm those birds before penning this stops the pen from getting a heavy worm egg l;oad that could be passed on.
we also give our flocks garlic powder in feed for 3 days every month, i swear by this for internal parasites yet i dont have a shread of proof it makes any difference, but my great great grandad did it, my great grandad did it, my grandad did it and my dad did it so i guess i do it
personaly i think a certain brand of very very exspensive organic wormer is a utter pile of chicken poo and a waste of money, if you want the organic root great but save the money and give your birds access to herbs like tyhme and nettle and garlic, let them pick and choose when they want a nibble
anyway i wasnt trying to say do this or do that or dont do this or dont do that, merely trying to pass on what little i know