What vegetables and fruits do cows eat?

Well, almost all of them.

the Shorter list is the ones to avoid, which are large quantities of onions, potatoes, rhubarbs, tomatoes, broccoli and cauliflower, although smaller amounts are tolerated reasonably well.

Also total avoidance of the nightshade plants like the pepper family are a good idea

Otherwise they will eat:

cabbages, kale, mangels, rutabaga's, turnips, carrots, parsnips, sugar beets, sweet potatoes, pumpkin

lettuce, squash, swede.

Apples, Oranges, bananas, cherries, all the berries, peaches, plums, apricots, Pears, cantaloupe, watermelons, grapes

coconut flesh, not whole.

plus a whole variety of trees and shrubs, like willows, poplars, comfrey

but should avoid pine needles - they will eat them just not good for them.

If feeding vegetables ideally shred them and sun dry them for less choke risk and help over the winter time feed.

I am sure I forgot some they can eat; these are the ones we grow and/or feed them.