A man I work with told me his son's farm eggs have weak yolks that break when he cracks the egg. This frustrates him because he likes fried eggs. I have a few hens that lay eggs with yolks that break easily, others are more firm and stand up to the frying pan. Any ideas on why the yolks would break easily? I have oyster shell out free choice for my hens and it makes a huge difference in the strength of the shell. Not sure what to do about the weak yolks. Thanks!