Cows are "prey" animals. They evolved in the grasslands and were subject to predation by lions or wolves or other large predators. In spite of our efforts to domesticate them, they retain the basic instincts of prey animals.
Recently I posted a photo on Facebook of a newborn baby calf that was lying curled up on the edge of a creek. I included the caption, "Pretend you can't see me. Momma says I can't move." That photo is below.
There was some concern expressed that something was wrong with the baby. Why would a mother hide her baby and then wander off and leave it? It is because she is protecting it.
Below is another example of a hidden baby. I spotted it from across the pasture and zoomed in at the highest magnification I could with my Nikon 55-300 mm lense. Can you see him lying in the fence line? His mother is about 400 yards away grazing -- pretending to ignore him.
Again, I am zoomed in at highest magnification. Now it is clear that it is a calf lying next to the fence. Each of the photos below is just a little bit closer.