I think there were 2 concerns being raised here.
#32 was regarding chickens eating horse feces after the horses had been medicated with Bute for treatment of ringworm. The concern was if traces of this medication would then show up in the chicken eggs. That owner should check with the manufacturer of the medication, or with a local vet... Or ? I don't really know who!
Post # 33 regards chickens who just eat feces. Animal feces contains lots of undigested nutrients. Like it or not, chickens will eat it when they find it. They will eat feces, as well as grains that are passed in the feces, and the insects found in the feces. They are also co-pastured with grazing animals to decrease the parasite load for the larger animals. By the time all of that material passes through the chicken's gut, and the chicken extracts the nutrient, and turns it into yummy eggs, it makes not a single bit of difference what the chicken has eaten. IMO, an egg from a chicken who has been ranging in a pasture with grazing animals is far better by all measures than an egg from a chicken who eats nothing but processed chicken feed.