According to the University of Washington, cows sleep for approximately 3.9 hours per day, meaning that they spend about 16.9 percent of the day sleeping. Adult humans sleep for approximately 8 hours per day, which represents 33.3 percent of the day. Human infants sleep approximately 16 hours per day.
While cows need relatively little sleep, giraffes sleep even less. On average, an adult giraffe sleeps just 1.9 hours per day. On the opposite end of the spectrum, brown bats sleep for 19.9 hours per day, giant armadillos sleep for 18.1 hours per day and North American opossums sleep for 18 hours per day.