If these eggs are being produced by more than one hen, you may have a flock nutrition issue to address. Hens that have had certain diseases will oftentimes produce misshapen eggs, and I suppose the same problem could interfere with the synthesis of the shell while being formed. If it is only one hen I would not be too concerned. But I would not hatch that hen\'s eggs in case it would be genetic - a propensity caused by some kind of mutation. That seems very unlikely, but even so I wouldn\'t chance it. Sorry I can\'t give a more \"concrete\" reponse.
Thanks Mike. It doesn\'t happen very often, but it has happened from more than one hen...certainly not on a regular basis, though. It\'s almost like there\'s too much calcification on the outside of the shell.
I doubt it\'s a nutrition issue, my ladies free range but always have 20% lay pellets available, plus crushed oyster shell, plus occasional treats (less than 5% of diet) such as a handful of scratch or some sunflower seeds, or leftover veggies or whatever.
Thanks for the thoughts, and I\'ll let you know if I get any more of these concrete eggs.
Liz in Utah