I have several different breeds in my flock and all seem fine except my Rhode Island Red hens. I have lost 3 in less than a week. First we thought they were getting egg bound from their eggs shells being too hard and too big so I cut back on the oyster shell I had been giving them. Then we thought maybe the roosters, even though they typically all got along as they've all been together since they were babies. But we took two of the four roosters out and put them in separate cages and still lost another one. I am noticing blood in a nesting box and 2 of the 3 have bloody bottoms and look like their vents are wide open. I'm confused as to why this is only happening to this breed and what it even could be?