Winter can be a difficult time for a small flock of chickens. There are several things you can do for them that will make it a little less of a struggle for both you and the chickens.
Water is the most important concern for chickens. They will generally drink about 2 pounds of water (about a quart) for every pound of feed they eat. Water is important for healthy digestion, temperature regulation, and also for egg production, since an egg is more than 70% water. Unfortunately, as will be discussed later, chickens will also excrete a great deal of water in their droppings, which can be a problem.
Chickens need to have fresh water at least daily. Heated bases for waterers are available. Other methods have been used to keep water thawed, as well. Heat lamps are often hung over the waterer. Highly insulated water containers are available that will keep warm water unfrozen for several hours. If none of these is available, fresh water should be provided twice daily for the chickens. Rubber pans can be helpful, so ice can be removed easily without damaging the pan. Another option often used is to have two waterers, so they can be alternated and the other one brought inside to thaw.
Chickens will need a considerable amount of feed, especially to keep warm in cold conditions. High energy feeds, such as grains and oilseeds (corn, scratch grains, sunflower seed, etc.) can be supplemented to provide extra energy. One should be somewhat cautious not to overdo this, however, since nutrient imbalances could occur. Excess energy can increase the risk of feather-pecking. If this starts, it is best to stop the supplementation and rely on a balanced complete feed. Many people also like to provide some plant material to their chickens over winter. This may help keep the chickens active throughout the day. Leafy hay, root vegetables, squash, pumpkins, etc. can be used for this.
Ventilation is very important for chickens year-round. As mentioned previously, chickens drink a lot of water, and excrete moist droppings. This moisture can be a problem if ventilation is not sufficient. Wet litter will produce ammonia that can be harmful to the chickens, and to you. Even fairly low levels of ammonia can be irritating to chickens and to the chicken owner. Damp conditions can also increase the incidence of respiratory diseases.
The challenge for a flock-owner is to balance the need for ventilation with the desire to keep some warmth in the coop. There is ongoing debate about the need for heat in a chicken coop. A large number of chickens will produce enough body heat collectively so that additional heat is likely not needed. A smaller flock is not able to do this, and many people will want to provide some source of heat. Without some added heat, the chickens will be very uncomfortable, egg production will decrease significantly, feed consumption will increase, and the chance of frostbitten tissues will increase. Safety is a key concern, however, and is often cited as a reason not to provide heat. Chicken houses are dusty, and chickens may knock things over, especially if disturbed. Great care should be taken to shield any heat source and to keep them clean and safe.
Whether heat is provided or not, ventilation is still important. At the very least, there must be some open area to allow fresh air in and stale, moist air out. A window can be left open a bit, or a vent can be added on top of the house. Ideally, air has an inlet and an outlet so some air movement can be attained within the house, without it being drafty.
Lighting is another important factor for winter. Hens normally lay eggs when days are long (in the spring and early summer), and then molt and stop laying eggs when days start to get short in the fall. Though a lot of selective breeding has been done to improve overall egg production, short days will still decrease egg production greatly. If artificial lights are used to keep the day length at about 14 hours or more per day, hens will generally keep laying eggs through the winter. Artificial lights are traditionally started around September 1, and continued until spring when the natural daylength reaches 14 hours. The light does not need to be overly bright, and excessively bright lights can increase the incidence of pecking. Light intensities of 1-3 foot-candles are normally suggested. An old rule of thumb is that the light just needs to be bright enough so you can read a newspaper.
If light bulbs are used as a heat source, it may be more important to keep them on 24 hours a day. While this is not optimal for peak egg production, it may be a necessary trade-off instead of having 14-15 hours of light, and 9-10 hours of extreme cold.
Keeping a deep layer of bedding can help insulate the floor and may help keep the coop slightly warmer. Any obviously wet areas of litter should be removed, but dry bedding can be left throughout the winter, and cleaned out in the spring.
Flock safety should not be neglected in the winter. Many predators will be hungry and looking for a chicken dinner. Air inlets and outlets should be covered with sturdy wire or screen to keep predators, as well as pests, out. Raccoons and other predators can squeeze through fairly small holes, so care must be taken to close these well.
Rodents and wild birds may also be looking for a warm place to stay and an easy food source. Stored feed should be kept in rodent-proof containers, and feeders should not be accessible to rodents or wild birds. Preventing these pests is important for good biosecurity.
Over the longer term, flock-owners may want to consider selecting a breed that is more suited to cold conditions. Chickens with smaller combs and wattles are less likely to suffer from frostbite. Breeds with crests and feathered feet can have problems with ice and snow buildup on these feathers, so those who want to raise these breeds should adjust their husbandry accordingly. Nipple waterers, for example, can help keep crested chickens from getting ice on their crests. Loose-feathered varieties may also be better insulated and stand the cold better than those with very tight feathering.
With a little pre-planning, keeping a flock of chickens through the winter can be done and the chickens should be able to handle it well.