There are a few things you can do to MINIMIZE exposure. (applies to all grazing/foraging animals/birds) Rotational grazing/free range is one. Removing droppings, eliminating/controlling intermediate hosts. (worms, flies, grasshoppers) Sounds almost impossible, especially with chickens, huh? Some worm eggs can survive months... months and months... waiting for the right conditions to hatch/infect host. They can also survive harsh conditions, AND most dewormers used (on any animal/fowl) only get ADULT stages of the worms... the egg and larvae stages are rarely affected by dewormers. So, those have to mature to adults in the chicken before you can kill them.
IMO, a consistent deworming rotation is best... reducing the number of eggs shed into the environment. But honestly, anything that grazes, forages and/or eats bugs is going to get worms. Simple as that. You will NEVER eliminate them completely...ever. Management is all you can do. Deworm on a schedule that's appropriate for your location, that's about all you can do.
Some people only deworm on an as needed basis. If/when they see any problems or symptoms. I prefer to deworm on a schedule. As with any of my livestock, I want the best feed conversion possible (among other things) and I won't feed worms!
Well, any more than I HAVE to....
IMO, by the time you SEE problems or symptoms of worm infestation, you've got a BIG infestation. (if you see worms in poop BEFORE any deworming treatment, that's likely a sign of a pretty decent infestation. You won't see worms in poop, hardly ever, until you deworm... any that are pooped out before a treatment are sick/dying/dead for some reason...there are lots more-- and 'healthy ones' don't get pooped out)
