I have 2 bantam Hamburg hens only 2 years old which were laying pretty good up until a few weeks ago. Now I find thin shelled eggs broken in the nest. The frequency of laying also appears to be down. They seem to be in good health and their diet has not changed. They get plenty of corn, bread, broccoli, canteloupe sprinkled with laying mash, grit and oyster shell. I have recently been adding powdered vitamins to their food and even digging up worms as treats. I cannot figure out why the eggs are defective! Any ideas would be appreciated.