As we head into February, and the temperatures dip into the negatives, a question we're often asked is: "at what point is it too cold for my horses to be outside?" I don't know about you, but when it hits -12 F, I sure don't want to be outside. My extremities get too cold, the exposed skin on my face starts to burn, my breath freezes instantly. But do our horses experience cold the same way?
The answer is no - horses are much better equipped for the cold than we are. They (mostly) develop thick fluffy coats which insulate them all around, better than any heavy jacket. And they have an internal furnace - the large colon, which digests the roughage in a horse's diet, produces a large amount of continuous heat. Finally, a horse's extremities are developed better for the cold than ours are. Below a horse's knees (carpi) or hocks, the limbs are made up of tendon, ligament, bone, and skin. Notice something missing? There's no muscle... which means a lot less tissue, and blood, to chill. Studies have been done on laminitis (heat and inflammation of the feet) which required horses to stand up to their knees in slushy ice water for DAYS. This not only helped prevent laminitis, but none of the horses suffered frostbite or any other such tissue damage on account of the cold.
What about the airway? Many human asthmatics will notice that their lungs are more reactive in cold weather than nice warm weather. We don't tend to see this change in horses; in fact, most horses with inflammatory airway disease (like heaves) are kept outside year-round (to decrease exposure to allergens such as dust), and most are symptom-free in the winter. Why the difference? I assume it's because a horse's nasal passages and trachea are so much longer than a human's. The air travels a greater distance across warm mucous membranes, and is likely warmed to nearly body temperature by the time it reaches the lungs, regardless of what temperature it starts out at.
So how cold is too cold? With a nice heavy haircoat (or thick winter blanket, especially in our thin-coated hot blooded horses who do not develop a good coat on their own), and some sort of shelter (a three-sided run-in shed), it should not get "too cold" in this area for a horse to be outside. Keep in mind that shelters should be placed to shield the horses from prevaling wind, and they should be large enough that all horses in a field can be sheltered at the same time. Watch for dominance patterns; the "low man on the totem pole" may be forced out of the shelter, even if there is plenty of room. Also, be more protective of older or thinner horses, and those with chronic illnesses. Keeping warm takes extra calories, so feel for ribs underneath those blankets or thick haircoats - if you can feel ribs easily, the horses are too thin and need more feed. (If you are feeding plenty of feed and your horse is not keeping weight on, have the teeth checked - if he can't chew it properly, all the hay in the world won't keep your horse plump).
All in all, with a heated water trough to keep ice at bay, a wind-blocking shelter, a heavy coat (or blanket), and enough hay to keep the colon chugging along, most adult horses will be happier outside than in a warm, snug barn. Thin horses may need additional blanketting and extra feed. Young foals (we're getting to that time of year again!) and horses of advanced age may need to be kept in during the coldest days. If your horse has a respiratory issue, pay attention to whether or not cold weather bothers him. You'll likely discover it doesn't, but if it does, you may ride less in cold weather and allow him to regulate his own level of exercise. Use common sense - if your horses look miserable, or are shivering, by all means bring them inside. But try to remember that they aren't human (fortunately for them!) and they experience the cold very differently from us. And then go inside, make a cup of hot chocolate, and watch them play in the snow. :-)