We often get asked whether it's ok for your hens to be laying strange shaped eggs. Yes, it is. Hens normally lay oddly shaped eggs when they first come into lay, while their egg laying system is getting used to functioning, and towards the end of their most fruitful laying period as they get a bit older.
Generally speaking, hens will lay small eggs (pullet eggs) which often have a normal sized yolk for a couple of weeks before they start laying normal sized eggs. If they come into lay later on because it's autumn or winter time, they can even start laying normal sized eggs from the start.
You can get huge double yolkers (ouch!), teeny tiny eggs which either have virtually no white or without a yolk (also called a Wind Egg), strange bubble eggs where the shell has not formed properly or shells which are misformed and rutted.
So long as the hens have plenty of oyster shell, layers pellets or mash and plenty of fresh water available, do not worry when you see the odd bubble egg or strange shaped egg. If you don't think your hen is eating the oyster shell, try changing where you give it to her. Put it in her food and throw it around on the floor.