We have several different roosts, and all of the chickens that got bumble foot were on the same roost that was the high one. They always roost in the same place. And all of them were the heavier ones. After we treated the bumblefoot and lowered the roosts we have not had a problem with bumble foot again, and that is the only change we had made. Therefore, I think it is safe to say that is what happened and can happen. We did a lot of research as to the causes and that was one of the main causes was a too high roost. The impact alone on a hard surface (ours was packed dirt but since then we have layed down straw) repeatedly is likely to results in bumble foot. One of the worst being our 15lb rooster