Chickens are well equipped to handle the cold. They do not need the heat lamp. Heat lamps have burned many coops to the ground. It also prevents the birds from acclimating to their environment and can cause death if you get a power failure and they are suddenly plunged into much colder temperatures.I had one in there for them because they like to sleep outside in the run at night. during the fall it gets cold
Chickens need protein to grow healthy feathers. What is the percentage of the protein in the feed you are giving them? How much do you feed for treats?