Eggs need protein in addition to calcium, and if new layers are producing more than a one-off shell-less egg, I would look to diet. Layer feed, unless it has 18% protein is not high enough in protein to finish a first-year layer's growth. They may appear close to full size at sixteen weeks, but they are still far from being full grown. Growth requires protein. So do making eggs. If there isn't enough protein in the diet, something is going to come up short.
Also, oyster shell alone isn't enough to build up calcium reserves. Vitamin D, in the form of sun exposure or added in the feed, is necessary for calcium absorption.
For these reasons, I discourage the feeding of layer feed until the hen is two years old and finished growing. In fact, many of us have dispensed with layer feed all together and just feed a 20% all flock feed to the entire flock all the time.
I would do as @TX Chick Noob has suggested and give calcium citrate with D for a few days until eggs are coming out with normal shells. Then offer oyster shell free choice but not scattered on the ground. Remember, oyster shell is calcium carbonate and it's water soluble, dissolving into a useless gummy paste when it gets wet. This is not the quality of calcium the hens can utilize.
Also, oyster shell alone isn't enough to build up calcium reserves. Vitamin D, in the form of sun exposure or added in the feed, is necessary for calcium absorption.
For these reasons, I discourage the feeding of layer feed until the hen is two years old and finished growing. In fact, many of us have dispensed with layer feed all together and just feed a 20% all flock feed to the entire flock all the time.
I would do as @TX Chick Noob has suggested and give calcium citrate with D for a few days until eggs are coming out with normal shells. Then offer oyster shell free choice but not scattered on the ground. Remember, oyster shell is calcium carbonate and it's water soluble, dissolving into a useless gummy paste when it gets wet. This is not the quality of calcium the hens can utilize.