In winter, many people blanket their horses, but blanketing can affect the amount of hay the horse consumes. Blanketing is controversial, especially in Texas as in most of Texas our winters are not really that cold, and blanketing can also have some unwanted side effects such as skin disease or overheating in some horses.
A recent study performed in Wisconsin by Dr. Michelle Deboer found that blanketed horses ate 8% less free choice hay than unblanketed horses and yet maintained normal body condition. The Horse publication reported that the researchers blanketed eight adult horses in a dry outdoor paddock in Wisconsin from December to January during which they did not blanket eight other horses in an adjacent paddock. Each group of horses had identical free choice hay. The researchers found that the blanketed horses’ weight and body condition remained the same but the horses with blankets ate less than horses without blankets and the difference was about 2 pounds of hay per day. So, horses voluntarily reduce hay intake when blanketed but this does not cause weight loss as the horses use less energy to keep warm and could even gain weight. Blankets can hide an individual’s body condition so you want to make sure the horse is not gaining or losing weight under the blanket. This study shows you could save a little money on hay but that would likely be offset by buying and maintaining a blanket.
I believe a blanket is not needed unless the temperature is freezing or lower or there is freezing rain. Then when the weather warms up, get the blanket off and allow the horses to get acclimated to the outside temperature. Realize this study was performed in Wisconsin and eight of these horses lived all winter without blankets with no health issues.