I have two ducks in with 10 chickens. The ducks lay on the ground, and their egg shells are really thin. The chicken eggs are fine, very normal, and are laid in the nesting box. This egg was on top of one of the roosts, so I don't think it was a duck, but it looks just like the eggs that are on the ground, only thinner shelled. I'm thinking vit d3 is called for but how to dose the ducks but not the hens and what product and dosage? Is anyone able to help me?