As the daylight hours grow shorter, your chickens will slow or stop their egg laying, and begin to molt. This is a natural process, not a sign of illness, however there are a few ways that you can help your chickens through this time.
Your chickens will need more protein in their diet to help them grow healthy feathers. You may wish to switch them to meat bird feed during this time, and supplement that with protein rich treats such as black oil sunflower seed or soybean meal. You can switch them back to their regular diet as spring approaches.
Losing feathers is a stressful time for the chickens, so try not to add any further stressors, such as new birds to the flock, or a new location for the coop. The new feathers are very sensitive and are easily broken, so try not to handle molting chickens any more than necessary.
A broody hen will put off molting until her chicks have hatched, and then will molt all at once, so be watchful of extra stress for that hen.