I have 9 approximately 5 week old chicks living together under a heat lamp. They are a mix of silkies, americanas, Rhode Island whites and reds, and a barred rock that is suppose to be a rooster. I am very worried about the barred rock because he is much smaller than all the others. He acts just the same as the others and eats well. Is he going to just be very small? What can I do to help him grow? Thank you! I can attach pics.