When cold weather arrives, one horse problem we are more concerned about than normal is colic. And although the weather here in Texas does not get as cold as it does up north, it is still cold enough to have an effect on the horses, and in fact, i think the effect in Texas may be greater than up north because our weather changes so much. We have days that are 70 degrees and the next day may be 30 degrees, and I believe this affects animals more than just constant cold.
The main reason colic increases in cold weather is that horses do not drink enough water and I think these horses just aren't thirsty in cold weather. Also, hay has less water in it than green grass in the pasture, so that is another area of decreased moisture. With dry areas in the intestine, feed dries out and an impaction develops, thereby causing colic pain. Poor quality hay is less digestible, which increases the chance of colic. Many times during the winter, horse owners increase the volume of the horse's feed to meet the energy demands, but this can upset their digestive tract and cause a decrease in function. Another concern is that many horses are kept in stalls in the winter due to the cold temperature. Standing in a stall may slow movement of the digestive tract, which also leads to an impaction.
Some options to increase water consumption are bringing warm water out to your horse or having heated water troughs or water bucket heaters. Soaking the hay in water may be helpful to increase your horse's water intake, and adding water to the feed will sometimes be effective if the horse will eat it. If you are going to increase feed, then increase the hay and not the concentrate. Finally, keep the horses out in the pasture as much as possible rather than in a stall.