Thehorse.com - Full Article
by: Heather Smith Thomas
December 07 2004, Article # 5301
Make sure horses have good access to water and are drinking. They drink less during cold or wet weather, but still need an adequate supply or they may become impacted. If water is quite cold or freezes and the horse isn't drinking enough, he'll eat less feed and may lose weight or be less able to keep warm. Horses will eat snow, nibbling a few bites of snow periodically while eating or grazing. A horse at pasture may get along fine if snow conditions are right for eating it easily (not hard and crusted), but there's always some risk for impaction.
If his manure becomes firm and dry instead of soft and moist, the horse is not getting adequate water. He won't eat all of his hay, though this clue may escape your notice if he's in a group and the other horses eat the hay he leaves. If he is dehydrated and not eating enough, his flanks and abdomen will draw up and he'll look gaunt.