Ridged Eggs

[hulson]

My two year old hen is laying hard shelled eggs, but with ridges around it. The ridges are getting more pronounced and deeper. She is on a premium diet and has a bowl of oyster shell always available. Again, the shells are not soft; they are very hard.

 

[Eggcessive]

There can be many reasons for this type of egg shell such as sub-clinical infectious bronchitis, defective shell gland, too much calcium, copper deficiency, heredity, and other reasons. I have one that lays one every other day. Here is some reading about eggs:
https://www.backyardchickens.com/a/common-egg-quality-problems
https://www.alltech.com/sites/default/files/alltech-egg-shell-quality-poster.pdf