01/17/2026
โ๏ธ Great little read on Piloerection.๐
โ๏ธ ๐๐ข๐ฅ๐จ๐๐ซ๐๐๐ญ๐ข๐จ๐ง: ๐๐ก๐ ๐๐จ๐ซ๐ฌ๐โ๐ฌ ๐๐ฎ๐ข๐ฅ๐ญ-๐๐ง ๐๐ข๐ง๐ญ๐๐ซ ๐๐ฅ๐๐ง๐ค๐๐ญ ๐ด
Time to bring back one of the very first topics I discussed on this page: piloerection. I write a lot about blanketing because it can be a great management tool when done well. But itโs also important to highlight how a horse naturally thermoregulates without human intervention!
When a mammal becomes cold, the goal is simple: conserve heat as efficiently as possible. This process begins with cold-sensitive thermoreceptors in the skin, which activate the sympathetic nervous system. That activation triggers the pilomotor reflex, similar to goosebumps in humans.
During this reflex, sympathetic nerves stimulate the arrector pili muscles to contract. These small smooth muscles attach the skin to the base of each hair follicle, and when they contract, the hair stands on end. This process, known as piloerection, allows air to be trapped between the hairs, creating an insulating layer that helps reduce heat loss.
I like to use a scuba diving analogy here. A wetsuit doesnโt keep you dry, instead, it traps a thin layer of water against your skin. Once that layer warms up, youโre no longer losing heat to fresh, cold water every second. Without it, your body would be trying (and failing) to warm an entire ocean.
Piloerection works the same way. By trapping a layer of air between the erect hairs, the horseโs skin isnโt constantly exposed to new cold air, which helps conserve body heat.
๐ฌ๏ธ๐๐ก๐๐ซ๐ ๐ญ๐ก๐ข๐ฌ ๐ฌ๐ฒ๐ฌ๐ญ๐๐ฆ ๐ข๐ฌ ๐๐จ๐ฆ๐ฉ๐ซ๐จ๐ฆ๐ข๐ฌ๐๐
Piloerection is effective, but itโs not foolproof. Wind and rain can significantly disrupt this process. Wind strips away the trapped air layer, and rain flattens the hair coat, preventing the hairs from standing up at all. This is likely why studies consistently show that horses seek shelter or prefer blankets during windy and wet conditions.
A wet hair coat is especially problematic. When the coat becomes saturated, the insulating air layer is lost, and water conducts heat away from the body far more efficiently than air. At that point, piloerection canโt function as intended, and heat loss increases rapidly.
๐งฃ๐๐ฅ๐๐ง๐ค๐๐ญ๐ข๐ง๐ , ๐ฉ๐ข๐ฅ๐จ๐๐ซ๐๐๐ญ๐ข๐จ๐ง, ๐๐ง๐ ๐ฆ๐จ๐ข๐ฌ๐ญ๐ฎ๐ซ๐
Blanketing can absolutely support horses in challenging conditions, but itโs important to recognize that when a horse is blanketed, piloerection no longer occurs. Whether thatโs because the horse is already warm enough or because the weight of the blanket physically interferes with hair elevation isnโt fully understood.
This has raised concerns about the use of uninsulated sheets in winter. While we donโt have a definitive answer yet, a pilot study I conducted two winters ago suggests moisture management may be the key issue. Sheets lack insulating fill that can absorb or buffer moisture generated beneath the blanket. As a result, damp air can become trapped against the coat and skin - and cold plus moisture is not a good combination.
In contrast, blankets with added fill can absorb some of this moisture, helping maintain a warmer, drier microclimate next to the horseโs body.
๐ง ๐๐จ ๐ฐ๐ก๐๐ญ ๐๐จ๐๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ฆ๐๐๐ง ๐ข๐ง ๐ฉ๐ซ๐๐๐ญ๐ข๐๐?
This doesnโt mean you shouldnโt blanket. It means that if you choose to blanket, the insulation provided must be equal to or greater than what the horse would achieve through piloerection alone. If that threshold isnโt met, we may actually be reducing thermal protection rather than improving it.
The challenge, of course, is that thereโs no one-size-fits-all answer. Weather conditions, wind, precipitation, individual horse characteristics, hair coat, metabolic rate, and blanket weight all interact. That complexity is exactly why blanketing should be viewed as an active management decision, not a set-and-forget solution.
Next time youโre at the barn on a cold day, take a moment to watch an unblanketed horse and notice the subtle ways they work to stay warm. Itโs a remarkable, and often overlooked, physiological process.
And if any blanketing companies out there want to collaborate on future research - you know where to find me!
Cheers,
Dr. DeBoer
