Because they like it.
No. Cows are herbivores, meaning that they are strictly plant-eating animals, not omnivores nor carnivores. Cows eat grass, hay and silage and should eat just grass, hay and silage.
Yes.
Yes. Hay is THE main staple of any cow's diet when not on pasture.
Cows do not eat (nor drink) milk. They drink water and eat forages like grass, hay, silage and grains.
cows eat grain, grass and hay
Grass, hay and sometimes grain.
Roughages including hay and grass.
They can, but it's not nearly as nutritious as grass or hay.
Cows are grown up; they are mature female bovines. They eat grass, hay, silage, and other forages, basically.
They can, but it's not nearly as nutritious as grass or hay.
If they were given a choice, they'd choose grass over hay any day. But during the winter months when there is no grass to eat, hay is their primary choice.