I have a white leghorn that has thin shells on her eggs. Almost every egg she lays has a hole in the end with cracks. The shell is extremely thin on that end but it doesn't break the membrane. They are on 16% layer feed, have free range of an 1/8 acre full of greens and bugs and have access to oyster shell. Is there anything else I can do to strengthen up her eggs? Here is a pic of an egg I got today...