I have chickens in two separate coops and runs. They are never mingled. I have noticed that most (but not all) of my chickens in both coops have lost weight. So much so that I can feel their keel bone. We live in the mid-south on the coastal plain. Our temps have been in the 50's during the day and in the low 30's at night. With the occasional warmer day or night. I don't supplement the coops with additional heat all night long. We do have lamps with 150 watt bulbs that are on for about 3 hours each evening. They give off some heat but are mostly there for the light and egg production. As far as I can see they are eating well. Maybe not quite the quantity that they were in the summer but eating. I have been feeding them private label, high quality layer crumbles from a local milling company. Into the feed I also mix alfalfa meal and turmeric and oyster shell. Several times a week I make them a mash with hard boiled egg or oatmeal in it. Poos seem to be normal. I'm not much for treats but I have given them a small sprinkling of scratch and crimped oats in the runs, every other day. Mostly to give them something for which they can peck around. I did worm them with ivermectin paste 3 weeks ago. I am dealing with something that is causing weight loss but there are no visible signs or symptoms that I can see, especially in the one coop. In the other I saw some mites during the day in the coop and run. They looked like chiggers to me and were orangey-red color. We stripped that coop, sprayed it down with permethrin 10%, changed the bedding sprinkled Seven 5% on bedding and stirred it in. That was on Thanksgiving Day. I have seen only a few mites since. If the mites that I saw during the day are the same blood sucking ones that attack at night, would this cause the weight loss? But I have other hens who have lost weight who are in a separate coop and haven't seen any mites there at all. Are these the same as the blood sucking mites? How can I tell the difference?