My original Khaki hen started having thin shells at about 1 year old. I noticed that the shells have a swirl where it seems that the calcium is not evenly distributed. Her daughter's eggs are the same way. What causes this? I am out of ideas how to make her eggs thick again. I have tried a couple different types of "oyster" shell, expensive laying feed with "egg building" formulation, even just good old multibreed flock raiser or all-flock type of feed. Everyone gets it, chickens, goose, and ducks. I don't have room for them to store feed and expect it to stay fresh. I usually have them on a new food for two months at least to see if it seems to be helping. I now feed a complete "layer" feed, a 5-grain scratch, and treat with bird seed, koi food and meal worms. I thought about somehow dissolving calcium in the duck's drinking water, but then I would have to remove their play water from their pens. Everyone knows how much ducks love their water. Lately I have been putting the duck with the thin shells out on the lawn to forage, but not every day. Perhaps it has helped a little but she isn't laying as much as she did before so it is hard to tell. When she started laying she laid an egg every day, perhaps skipping only one or two days a month. Now, she only lays eggs that I can find (I suspect some are just too thin and are broken and eaten) about 3 days a week. She just had her second birthday.