While Mother Nature throws every kind of winter weather element at the Owyhee herd, She also gives them the protection they need against it.
The shortening of days and less daylight in autumn trigger photoreceptors in the eyes, and the cooling temperatures trigger skin sensors, which signal hair follicles to start growing a winter coat. As long as humans don't interfere by blanketing, Mother Nature and the Horse usually work it out as to the necessary thickness of the coat.
When temperatures plunge, arrector pili muscles attached to hair follicles in that winter coat contract, and the hairs stand on end, trapping air and helping the horse retain heat. Morning comes and the horses turn broadside to the sun, exposing more surface area to quickly absorb more warmth that the hairs catch and hold against their bodies.
There's no barn out here in the wilds of Owyhee, but the horses will cluster together, or back up to a small rise of sagebrush to get out of the wind. We're fortunate that it doesn't rain too much here when the temperature hovers around freezing, and even when snow piles up on horse bodies, if the snow is dry and the wind isn't fierce, the horse coats will still stay fluffed up enough and keep the horses warm under the snow.
They have a limitless supply of hay to eat (and they're all maintaining good weight),
and thawed water to drink (with a water heater in the trough);
with adequate food and water, and shelter from wind and rain, the horses stay comfortable over the winter, no matter what feelings we might project on them (like looking out the window, thinking 'It's COLD out there, so the horses must be freezing!").
The horse coats are thick this winter, and what with the ultra-cold temperatures the last couple of weeks, it's good to be a hairy horse in Owyhee.