[changoplatanero]

What about when the horse is sleeping?

[rramadass]

See https://news.ycombinator.com/item?id=48247471

[cuechan]

I guess when the horse lays down the pumping force from the heart is enough to pump the blood back. Much less gravity to work against

[raffael_de]

horses sleep in a standing position.

(https://www.petmd.com/horse/do-horses-sleep-standing)

[koziserek]

then you dont need that much circulation.