Broody Hen Hatch with Yolk Sac Problems

Have a broody hen who has hatched three chicks so far. This story is kind of sad and gross, so I think a warning is in order. The first one evidently died after an unabsorbed yolk sac burst. I found it after it had died and ants were eating the yolk. The second chick is doing really well with no issues at all. The third one also has a small, unabsorbed yolk sac that ants were all over. After I relocated the hen, unhatched eggs and the chicks, I cleaned out the entire coop, sprayed the area with ant killer, let it dry and then sprayed outside the coop as well and re-littered inside. Then I took the poor baby, gently washed the yolk sac area and applied some antibiotic cream. So far, he seems a little better and I am so happy about that. I just feel so guilty about the ants. I have never had a problem with them before. Anyway, why would two out of three be born with unabsorbed yolks? This is the first time I have had broody hens so I have a lot to learn, but somehow I thought the natural way would be, well, easier. I've read other posts about the unabsorbed yolk sac and I guess, sometimes they live and sometimes they don't, but, two out of three chicks seems like pretty bad odds. Is there something I could have done to prevent this? I didn't intervene in any way. Thanks for your help.