So nice of you to rescue the battery hens. I've gotten some soft shells eggs lately but I have new pullets. I hope this changes as it cannot be a sign of old age in a pullet. The layer crumble has 16% protein and is supposed to have enough calcium in it. I could add calcium but the directions on the feed bag says not to do that because there is enough and too much calcium could cause liver damage. I've read lots here on this forum chickens only eat what they need, but I've seen my hens stuff themselves way to much one time when there feed got rain on it. It gave them huge poops and then a soft egg followed. Then I thought maybe they were getting too much greenery (mostly clover) as one had loose, green poop, and then she laid two eggs, both soft, that were connected.
One time I gave them cooked egg, chopped small and they loved that. They seem to be craving protein items as they go crazy if I give them a mix of protein things (chopped turkey, cottage cheese, meal worms, egg, and a light sprinkle of powdered calcium (even though my feed instructions said not to - but it is a tiny amount). Today they mostly just had their crumbles since I had the huge poop - soft egg - green poop issues yesterday. More normal stools today, but no eggs. I'll see what tomorrow brings. Two of them should lay tomorrow - they are due. The 3rd chicken (Rita) is not yet old enough.
I read you can eat the soft eggs if they are intact but so far I've tossed all but one of them. That one I cooked and fed back to the chickens (in which my sister promptly called them cannibals). Geez!