Daily rest time is important to cows for many reasons. It’s their version of REM sleep, they get their weight off their feet, ruminate more, and resting enhances mammary blood flow. Cows always lie on their chests so that their digestion is not impaired. 

Adult cattle need about 12 hours of rest per day and sleep for about 4 hours per day, mainly during the night time. Sleep, especially REM sleep (rapid eye movement sleep), occurs most often when the cow is resting with her neck relaxed with the head resting on the flank. Cows well adapted to their surroundings rarely engage in sleep whilst standing.