Hay is fermented in the hindgut, and that fermentation gives off a long-lasting heat.
Horses can be amazingly hardy. On a below-freezing day, your horse can stay warm and snug. So warm, in fact, that if you put your bare hands into his coat, you can actually warm them up. It's hard to imagine how a horse can keep himself comfortable when you are bundled up in so many layers it looks as if you could mount an expedition to the Arctic Circle!
Your horse is very adept at keeping himself warm; in fact, it's easier for him to warm up than cool down. He has more than one way to keep warm, but essentially, he is his own furnace. And with furnaces, if you put in the right fuel, heat is created. You can help kick-start that furnace in your horse by providing the proper fuel. For the horse, that fuel is food--and some foods are better for this purpose than others.
But first, let's look at some of the ways horses stay warm.
"In the fall, horses that have adequate feed supplies are beginning to put on more body fat, creating insulation and stored energy," says Bob Coleman, PhD, BSc, assistant professor and extension horse specialist at the University of Kentucky, in Lexington.
Horses increase in body mass at the time when there is good forage. Then, when Mother Nature dumps a lot of snow or when the grass isn't very good, they'll have stored calories to keep away cold and hunger, if needed. Although this is probably an evolutionary response, don't count on an extra-chubby horse being able to fend for himself in the winter. That extra layer of fat might help, but it burns very quickly in cold conditions.
Despite some of our best attempts to stop it, our horses also grow a longer hair coat to keep warm. Horses grow their coats when the days get shorter, not when the days get colder (as many people believe).
"Change in daylight has a greater effect on growing a coat than change in temperature," says Coleman. "The coat has to develop before the temperature gets cold. I grew up in western Canada, and our horses started growing winter hair in September."
But your horse becoming a wooly mammoth in winter isn't the "be all and end all." That coat might protect him when the snow falls and the temperature drops, but a rain storm coupled with the cold can take away the insulating factor of your horse's coat. In those conditions, your horse will also burn more calories to stay warm, thus depleting his stored layer of fat pretty quickly.
Still, horses have a third way to keep warm. And that is by eating.
Fuel the Furnace
Humans often think a nice restoring cup of hot tea or a steaming bowl of oatmeal will warm us on cold days, but it doesn't work that way for our horses. Hot food, such as a warm bran mash, might temporarily knock the chill off, but it won't help him stay toasty throughout the night. What will help keep those fires stoked is hay.
"It is how they digest hay that creates the heat," says Coleman.
Hay is fermented in the hindgut, and that fermentation gives off a long-lasting heat. This is much like how steam rises from your fermenting manure pile.
"Horses use that heat to maintain core body temperature," says Coleman. "So as a horse owner, you're stoking the furnace by feeding them a good-quality hay that they can digest and gather nutrients from."
Coleman also adds that forage has to be of good quality. "The better the quality of the forage, the more they can eat and the more they will eat," says Coleman.
Any good-quality hay that you can get locally will fit the bill. "As long as it wasn't overly mature when it was harvested and has a high leaf-to-stem ratio, and absolutely no dust and mold," says Coleman. "Then after that, if you are in an area where you can get reasonably good alfalfa/orchardgrass hay, that would be great. If you are in an area that allows for growing high-quality timothy hay, then that is equally good."
Grain still has plenty to offer in winter, if the quality is good. However, many people think that grains, particularly corn, are "warming" feeds. The truth is, a small amount of high-energy feed will only keep a horse warm for a short time. With hay you get calories, but also heat from digestion.
"Grain helps, but it's easier to break down and it won't cause that heat of fermentation," says Coleman. "There are readily available calories from a grain ration that should be part of the maintenance pack, but I would still base the diet largely on hay."
Which Horses Benefit?
The horse living in a stable isn't very likely to spend much time out-of-doors in inclement weather. More likely, he'll only get turned out when the sun is out or the weather is calm, and then only for a few hours. A horse kept in a warm stable environment "under wraps" doesn't need to generate his own warmth as much as a horse kept outside in all weather. But if your horse will be turned out until the spring thaw, your responsibility will be to give him every chance of staying comfortable.
Feeding for internal combustion is most critical for the older horse living outside. "It's very important that you don't let an elderly horse lose weight and that you are providing him with a readily available source of energy," says Coleman. "Letting a horse get down in weight in the winter is very hard on him."
In more temperate zones, there still might be grass to graze in pastures during winter, and even winter pasture can provide some nutrients. "But the level of nutrition can be low," says Coleman. "If horse owners have managed their pastures in such a fashion as to have a good growth of grass before winter sets in, then mature horses will do reasonably well grazing the stock-piled forage. Some grasses stockpile better than others, so owners need to talk to their county extension agent for advice."
Also remember that as snow gets deeper, horses have to paw through it to get to the grass. This extra work increases the horse's energy requirements. Freezing rain and ice storms can make grass impossible to graze. Coleman adds that horses should never be fed on the ground because of waste.
"Feeding on the ground can result in a loss of up to 25% of the feed," he advises. "But if you feed in a suitable feeder, you will reduce this problem."
Changing Your Program
Today people are bombarded with supplements (herbal and otherwise), different feed mixtures, and other additives; anyone can become easily confused about what to feed their horses. In the winter, try not to get complicated. Coleman says the easiest thing to do is to keep with your program and simply increase the horse's hay.
"It will all be predicated on the quality of the hay--and old Nellie can only eat so much!" says Coleman.
As a general rule of thumb, a horse needs to eat at least the equivalent of 2% of his body weight in terms of dry matter. So a 1,100-pound horse would need to eat approximately 25 pounds of hay to meet his daily requirement. An extra five pounds of hay will raise a horse's body temperature by 1° Fahrenheit for up to four hours.
Keeping Track of Condition
A cold horse is a hungry horse which will burn more calories to try and stay warm. You can keep track of how your horse is doing and whether your feed amount is on track by continually "body condition scoring" your horse. Body condition scoring is a simple system that was developed in the early 1980s at Texas A&M University. It assesses body fat on a scale of 1 to 9, with 1 being emaciated and 9 being extremely obese. The system has you analyze body fat coverage over the ribs, behind the shoulder, over the withers, back, and tailhead, and up the neck by feel and by sight.
"Basically, you run your hands over these areas and ask yourself if you can feel any bones, then use the guidelines to come up with a score," explains Coleman. "The system has a visual component, too. But once we get into winter and horses have long hair, the visual component becomes difficult and that is where people get into trouble. They look at the horses over the fence and notice their horses are big and hairy, so all must be well. In truth, that horse can be quite thin under his coat."
Keeping track of your horse's body condition every few weeks or monthly during winter will tell you if he's gaining or losing weight, so you can adjust feed accordingly.
It's interesting that horses in low condition will actually begin growing a longer hair coat. It's important to run your hands over the horse's body, particularly over the rib cage. If you can feel bones prominently under the skin, you need to increase the feed ration. If you are consistent and follow the guidelines, you'll know if you're getting enough nutrients into him.
"My preference is that if a horse is wintering outside, I'd like him to be in a body condition score of 6 or 7, carrying a little extra," says Coleman.
Don't Forget the Water
To help your horse keep his core body temperature up, you must make sure that his digestion is able to function at its peak. That means making sure he has a readily available source of drinkable water. That, says Coleman, does not include snow.
"Horses need to have a certain amount of water for the digestion process," he explains. "And I think people will come back with historical anecdotes about the myth of horses eating snow. I used to hear it all the time: 'My grandfather turned his horse out into the pasture and they wintered fine; they never drank water, they ate snow.' If you are in a position where your horse is being fed hay and he has to eat snow for his water, he won't be able to eat enough snow to compensate for the amount of water he needs for digestion and hydration."
It also was believed that eating snow cooled the horse's body, but studies done with beef cattle showed that lots of snow had to be consumed at one time before the core body temperature was cooled. Cold water, however, is a different story.
"There are some water sources that horses drink from that may prove the cooling theory correct," says Coleman. "If you think how cold some water can get before it freezes, a belly full of that would probably change his core temp."
A bucket of half-frozen water will not fulfill your horse's needs; he needs unfrozen water that is free of slush and snow. It's even better if you have taken the chill off. If your horse is going to winter outside, you'll need to invest in an automatic waterer with a heater. Coleman suggests that you set the water temperature to 37-40°F (2.7-4.4°C).
The colder the weather gets, the more calories your horse will burn to stay warm. If you see the thermometer dropping, the best way you can help your horse stay warm is by tossing him another flake of hay.
About the Author
Sharon Biggs Waller is a freelance writer for equine science and human interest publications. Her work has appeared in several publications and on several websites, and she is a classical dressage instructor.