Notice the steam rising from the pile of hay? Look closely. You can see vapor, illuminated by the rays of the sun, rising off this pile. 

This is the boar and sows' bed. It is comprised of a couple thousand pounds of hay and straw. How does it steam and create heat in the middle of winter? The answer is in active composting.

HOW ACTIVE COMPOSTING WORKS

The lower layer of this pile is damp from rain and melting snow. And it is in contact with the dirt beneath. The pigs, while fairly tidy, will often urinate in their bed. This urine is loaded with nitrogen and goes immediately to the bottom of the pile with the other damp hay.

With the combination of carbon, nitrogen and moisture, this layer has all the makings of a beautiful compost pile. The pigs even scoot and turn it periodically. This composting hay will reach temperatures well over 100° Fahrenheit! 

HOW THE HEAT KEEPS THE PIGS COMFORTABLE

Above this hot layer is the deep, dry hay where the pigs sleep. Basically, it is nature's heated, Sleep Number bed. If the pigs want more heat, they simply burrow deeper in the pile. If they want it softer (or a little cooler), they fluff it up.

The pigs know how to make a bed better than most teenagers (maybe). No matter what winter brings, they'll get a toasty warm night's sleep.