How do the pigs at Sparrow Hill Farm stay warm when it's cold outside?

They have a healthy layer of fat just under the skin. This is their insulation blanket for the wintertime.

Pigs do not have the thick layer of wool like the sheep or a thick coat of hair like the cows. They do have a bit of hair which does help some. But they primarily rely on a fat layer to keep them warm.

Have you ever seen pictures of seals sitting on the ice with no fur at all? They stay toasty warm with just a layer of fat. Pigs are kind of like a hairy land seal. :) 

The pigs also get deep piles of hay and straw to bed down in. The straw starts composting through the winter creating even more heat. When they bed down for the night, they also leverage the heat of the community.

Pigs are big snugglers. They lay together in a pile of sorts. That way if there is one that has a bit less fat than the others, they don't get shortchanged on the heat. It's the opposite of the summer where they lay all spread out in the shade to stay cool. They have it figured out and only get a little help from their farmers.