Not really feasible in large (1/2 acre or more) fields, but paddocks and pens really oughta be picked up regularly, at least the worst of it, not just for health but for footing reasons too.
My horses have about 5 acres so although they live out 24/7 I don't make any attempt to pick poo in the summer (it'd be impossible anyhow), I just let the roughs be roughs (don't drag or mow 'em) and they don't graze there so it controls the parasite egg problem *that* way.
However I do clean around the run-in shed every day during the winter (i.e. for whatever part of year they are spending more time there, which pretty well coincides with the part of the year when insects are not breaking down the poo piles, too). Not so much for parasite reasons, although there is that, but just to prevent MUD! Takes me about 15 minutes on a typical day in the winter, or more if it's been a horrible blizzard and they've spent 24 hrs hunkered down in the shed, or when the poo is frozen hard onto the ground and needs to be whammed off with a shovel <hate that!>.
Pat