Neighboring Horse Farm

Nearly across the street from our Le Bic house is a horse farm with beautiful white and brown horses (and one black one) along with an old barn. There's pasture for the horses. The surrounding landscape is mostly hayfields with scattered patches of forest.
I enjoy walking by the horses each morning. They seem curious about me and my dog Woody, sometimes coming up to the fence to get a closer look (and probably hoping to get a treat).
This morning was a bit different, as most of the horses were lying down in the far field. Were they sleeping? I could not tell. But I do know that virtually all animals sleep in some fashion. I suspect horses can sleep standing up so they don't need to lie down for sleep to occur. I'd like to learn more about the sleep patterns of horses.

Our neighbors horses