Because they want to or feel like it.
cows eat grass
Cows
No. Cows EAT grass. They do not "have" grass.
French cows eat grass.
Cows
Cows will eat long grass. Haven't you ever heard, "The cow's in the corn?" Corn is a tall grass.
Cows don't eat animals, they eat grass they are herbivores.
No. Cows don't lay down when it rains: this is a myth. Also, cattle really don't care whether the grass they eat is wet or dry. Just as long as it tastes good or is palatable, then they'll eat it.
humans....we eat cows and cows eat grass...
Grass
no they eat grass
Grass