Okay, so I have read all about giving egg shells back to hens. I have 11 chicks (ages 3 weeks through 8 weeks aproximately) right now and today I am making several large egg casseroles. I will have 4 dozen egg shells from this process. Can I / Should I: grind up the shells an mix them in with their food or offer as a treat? OR, are they to young and this calcium isn't good for them. thanks in advance!