For a couple of years, I wondered why my Siberians chose to lay out in the sun and bake. I’m talking summer in Virginia! Dogs that laugh and play at -30F laying out in the sun baking themselves. I had to drag them in panting and their fur was hot to the touch.
I went researching this weird habit and it turns out all furry mammals do this. This is how they get vitamin D3. If you want to read the mechanics of how this works the link is last. The bottom line is skin oil is converted into vitamin D3 by the sun. For humans, it is absorbed into the skin. If you have fur like Uncle Bill then it is absorbed by the fur. The dogs lick their fur and get the vitamin D3 orally. Fortunately, we’ve never seen Uncle Bill do this!