We've always had a bloody egg every now and then, but lately there's a couple every day - pretty bloody, too. Why does this happen? We have a rooster, the hens are all healthy, though they have been confined for several weeks to the coop and pen due to several feet of snow in and around the pen.
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I'd suggest you check "blood spots" at this link. I think it can help you.
Egg Quality Handbook
I kind of suspect genetics and maybe a vitamin problem, but you are there looking at them and the conditions. All I can do si make a wild guess.