It won't hurt them if they got into it - only if they continued to eat it for a length of time. A lot of people (including me) don't ever feed layer due to the high calcium content. As another poster stated, it is hard on their organs... it is especially hard on roosters and silkies. Since I currently have pullets, roos, silkies and various breeds of layer hens, I only use a grower/flock raiser and then just supply oyster shell on the side. Then, they can regulate their own calcium and my boys and silkies don't get too much. When I have new chicks in the flock, everyone just gets chick starter for a few weeks, then back to the grower! Hope that helps!