This is one of two Rhode Island Red hens that we have with black spots on her comb and wattles. All the hens are 22-weeks old, raised by us on Purina Medicated Start & Grow since they were four days old and laying each day consistently for the last three weeks. We also have a Black Sex-linked hen and Easter Egger that do not have black spots on their comb and wattles. These spots just appeared in the past week, after I changed feed to Purina Layena Crumbles. We tried wiping the spots off with a warm damp cloth and did get some residue on the cloth, but there is no sign of pecking or damage on the comb. What could cause these black spots on the Reds and not the others breeds?