I have a 2 year old hen who is consistently laying very soft or un-shelled eggs. She has free choice oyster shells, layer feed, regular low salt content water. She usually lays the egg in question on the roost, so they either come late in the day or early in the morning. Anyway, she used to lay hard-shelled eggs. Do the egg shell glands "wear out"? At this point, I am guessing that it won't go away, but was interested to find if it is due to age or something else I haven't considered. She is either a hatchery Barred Rock or a hatchery Production Red. I haven't figured out which one it is just yet. Any thoughts would be appreciated. Thanks!