According to ANTRANIK, the reason dogs lay in the sun is because it helps them increase their levels of Vitamin D3. Both humans and animals need Vitamin D for healthy bones and joints, but dogs do not typically get vitamins from the foods they eat.
Vitamin D3 functions like a hormone. It helps the body regulate calcium levels and metabolism. According to Pekinews, humans can obtain Vitamin D3 after spending just 10 minutes outside in the sunshine. Dogs lay in the sun and absorb UV rays, which react with the natural oils on their skin and turns into Vitamin D3. The dog later licks his fur to clean himself, which results in the dog ingesting the vitamin. If the dog did not clean himself, the natural oils would remain hidden under his fur and later dissipate. Pets that don't properly clean themselves should see a veterinarian, as this lack of cleaning might indicate a serious health problem. Both dogs and cats lay in the sun because they enjoy the sunshine and the warm feeling on their bodies, but those animals also receive healthy benefits from laying in the sun. Pet owners should give their pets access to fresh air and sunshine every day.