Good quality hay is the most important winter feed for horses. In other words, a 1000 pound horse, should be given 10 - 15 pounds of hay per day. Raise this amount if the hay is of poorer quality. While hay can meet the nutritional requirements for most older or less active horses, grain supplementation may be needed for more active or growing horses. Make sure that your horses remain in a satisfactory body condition through out the year.
Water is often the most overlooked nutrient.
Water intake will depend mainly on the dry matter content of the horse's diet. Normally a 1000 pound horse will consume around 10 gallons of water per day. Be sure to check the water source to insure that it is not frozen on cold nights. Horses will consume adequate amounts of water if the water temperature is above 45 degrees. It is important to realize that a reduction in water intake can lead to colic.