One of my chicks hatched out with the yolk sac attached to it's navel, and I don't mean partially absorbed, it was hanging on outside and it has a flat little abdomen. The yolk sac was brownish-yellow and it burst when the little guy tried to kick out of the egg. I wrapped the whole thing up carefully in a cloth and put it in a coffee mug in the brooder so it can't kick anymore. It seems to be doing fine. Anyone else have experience with this issue?