If you are still seeing bloody poo after treating for 5 days with Corid that is
NOT normal.
When I have used Corid the bloody poo is always gone within 24 hours. There are 9 strains that affect chickens and resistance can exist.
Read this thread, but do read all of it before making decisions as there are some reversals:
https://www.backyardchickens.com/t/758621/coccidiosis-sulmet-or-corrid
You mention that your hens are laying. They should be immune to cocci by now. So either they have been exposed to a new strain of cocci by bringing it onto your property from new addtions or equipment/shoes, or they are immunocompromised, I am guessing.
Do they have worms/mites/lice? Are they ill from something else that would knock them down?
I have read that same info. you have, but I would not eat the eggs from hens with bloody poo.
There is also necrotic enteritis:
http://edis.ifas.ufl.edu/ps044
This mentions no laying hens and no chickens over 16 weeks. That was not addressed in the above linked thread I provided. I have never given this medication. I would not advise using it then after reading what this link says because of your hens being of laying age.
https://www.mcmurrayhatchery.com/sulfadimethox_albon_.html
It may be worth your while to take a poo sample to a vet for him/her to check it for cocci/bacteria/worms. I would call ahead to find out cost/whether they will do it though if interested.
False negatives are possible on the worms test.
