what breed do you have?
the drop in temp at night sends my rosie into a moult, the others follow. It could be lice or red mites they are leathal things.
Apple cider vinigar in the water and poultry spice in the food will boost their system up also feeding greens in the afternoon.
Are they due to be wormed, normaly done twice a year. I do spring and autumn.
First signs of something not right is not laying.
hope this helps