If you are mixing the eggshells and oyster shell into their feed, I would stop doing it that way and instead give it separately in another feeder. Have it available all the time, free choice so they can take what they need. Needs can vary depending on the age of the bird, how often they lay, time of year, etc. Allowing them to take it free choice may stop the deposits as that hen may need a bit less. Some of my older birds will start getting thinner shells with no apparent health problems. 'Laying cycle' refers to the changing seasons and the effects on their laying. Young birds are more apt to lay year round (can also depend on breed) and as they get older they will often slow or stop during the winter months when the hours of daylight are reduced. Then in the spring as the days get longer they will begin to lay again, or frequency will increase. The 'time off' many times will get longer with age. It's natures way of giving their body a bit of a rest. The only way to prevent that is with supplemental light, which will encourage them to keep laying year round, but will also likely shorten their lives. So during those times when they are going into or out of lay, glitches can happen.
