01/17/2026
❄️ 𝐏𝐢𝐥𝐨𝐞𝐫𝐞𝐜𝐭𝐢𝐨𝐧: 𝐓𝐡𝐞 𝐇𝐨𝐫𝐬𝐞’𝐬 𝐁𝐮𝐢𝐥𝐭-𝐈𝐧 𝐖𝐢𝐧𝐭𝐞𝐫 𝐁𝐥𝐚𝐧𝐤𝐞𝐭 🐴
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 it’s 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 doesn’t keep you dry, instead, it traps a thin layer of water against your skin. Once that layer warms up, you’re 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 horse’s skin isn’t constantly exposed to new cold air, which helps conserve body heat.
🌬️𝐖𝐡𝐞𝐫𝐞 𝐭𝐡𝐢𝐬 𝐬𝐲𝐬𝐭𝐞𝐦 𝐢𝐬 𝐜𝐨𝐦𝐩𝐫𝐨𝐦𝐢𝐬𝐞𝐝
Piloerection is effective, but it’s 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 can’t function as intended, and heat loss increases rapidly.
🧣𝐁𝐥𝐚𝐧𝐤𝐞𝐭𝐢𝐧𝐠, 𝐩𝐢𝐥𝐨𝐞𝐫𝐞𝐜𝐭𝐢𝐨𝐧, 𝐚𝐧𝐝 𝐦𝐨𝐢𝐬𝐭𝐮𝐫𝐞
Blanketing can absolutely support horses in challenging conditions, but it’s important to recognize that when a horse is blanketed, piloerection no longer occurs. Whether that’s because the horse is already warm enough or because the weight of the blanket physically interferes with hair elevation isn’t fully understood.
This has raised concerns about the use of uninsulated sheets in winter. While we don’t 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 horse’s body.
🧠𝐒𝐨 𝐰𝐡𝐚𝐭 𝐝𝐨𝐞𝐬 𝐭𝐡𝐢𝐬 𝐦𝐞𝐚𝐧 𝐢𝐧 𝐩𝐫𝐚𝐜𝐭𝐢𝐜𝐞?
This doesn’t mean you shouldn’t 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 isn’t met, we may actually be reducing thermal protection rather than improving it.
The challenge, of course, is that there’s 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 you’re 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. It’s 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
