Before I brought my horses home, I would tell my boarding stable operator to blanket my horses when the highs for the day were 40 or less. I felt I was being compassionate. If I was chilled, they would be, right?
But after I brought them home, the next winter I was able to read them well enough to try them without blankets and look for behaviors (running, crabbiness and shivering) suggesting they were cold and feel reasonably confident of detecting it. Day after day I watched the temps slipping further and further below my old level and the horses were fine. They ate more (about 150%) and had occasional short bouts showing cold symptoms, and then their hair would catch up within a day or so.
One time I put a windbreaker sheet on my reining horse and found it disarranged in the morning – as I unfastened it he reached over and yanked it off. I tried to put one on our ex-ranch horse and he tore it off twice before I could fasten it. These were behaviors they had never performed before.
I kept waiting, but it wasn’t until -7 (F) that they showed cold behaviors. That was the low for the winter. so I was never able to find out if they would have adapted. But it’s possible.
As for the idea of wetness – yes, if it gets through the coat, they can get cold. But a normal coat can carry surprising snow load or a surprising exposure to rain before the liquid touches the skin. You can tell, because the snow doesn’t melt. Resistance to rain is harder to see, but is certainly improved by not bathing your horse – of course, brushing is important – and can be improved by feeding horses higher fat diets like rice bran that support the skin and hair oils they need to be water repellent.
Horses need shelter in some circumstances, ideally outside with at least some freedom of movement. Yet when they have this, they often seem to stand inexplicably out in rain and snow. Of course, the reason they do this is that the weather doesn’t bother them any more than it would bother us if we were dipped in water-resistant fleece. When it bothers them, they go in.
Never blanket? Well, probably not. If you don’t have shelter, you may sometimes need to windbreaker / rain blanket. Have shelter but you’re getting horizontal sleet in 30MPH winds for a day or two? Might want to bring horses in or blanket with the windbreaker / rain blanket. But while the extensive blanketing does not permanently reduce hair coat, it is true that exposed areas will grow more and longer hair than blanketed areas, so early blanketing can affect the possibility of the horse being unblanketed later in the winter.
Now, of course, I look back on my old blanketing guidelines and shake my head at how misguided I was. Horses weigh a thousand pounds or more. Their volume to surface area is so different from ours, that for them shedding heat is more problematic than retaining it. Their coats are like a windbreaker over fleece with a significant water resistance, and the ability to retain so much heat that the temperature at the surface is below freezing and a scant fraction of an inch below that is over 70 degrees, rising to the 90s of body temperature in an even shorter further distance. Horses can stand in the snow and be covered with the stuff and it’s not melting on their fur. That’s very alien to us… bareskinned monkey descendants from the tropics trying to live in difficult and cold places, trying to retain heat in our tiny bodies.
But do remember that you need restraint to give horses the chance to grow out their hair. Pre-winter weather fluctuations can lead to temperature drops that are too fast for their adaptation to keep up. But if you blanket at that time, you damage the opportunity for the weather to signal the horses’ follicles to grow more and better hair. The weather will rebound to average and the horses’ coat will catch up and they will be ready for the real cold to come.
Horses are not people and we do them a typical disservice by judging how they feel about cold through projecting how we feel about the temperature. Remember to think of horses as horses, watch, test and learn, don’t rush to action – and you can help them live as natural and right a life as possible – which will make their minds tough, happy and relaxed.