Are they breaking the eggs open? This can be a hard habit for them to stop once they learn. There's no exact cause but there are few solutions. You can try putting fake eggs like plastic ones with rocks for eggs or wooden ones so they try to break them open they may learn that they can't. Also, you can make an egg chute sort of thing so once they lay, the egg goes somewhere else so they have no access to it. However, if you aren't able to fix it, you may have to cull them. Sorry
I don't think it's about feed, it's mostly if they learn to. I used to not separate eggs from my compost for chickens and they would drink the spare yolks because I don't eat them all. Mine have never broken their own eggs. Sorry