Cows, Vegetarian, Protein

I eat much less meat than before. So I begin to worry, would I lack enough protein? This worry drove me go online and search "How do vegetarians get protein?" The fancy web gave me answers including "dairy products, eggs, beans, and nuts".

Fine, I'll eat those stuff. But wait a minute, how do cows get protein?

Isn't it that they just eat grass?? Oh, no, I remembered a lot of corn produced in US are fed to cattle as well. Okay, let me find out what else they eat.

After checking out Wikipedia, yes, cows do eat corn (or silage), and even beans (or more appropriate, legumes)! hmm.. interesting.. however..

"For pasture-fed animals, grass is the forage that composes all or at least the great majority of their diet."

Eh.. doesn't this mean that there still exist certain cows only eating grass? And it turns out people even have debated over what should be fed to cattle. It seems that the more grass the cow eat, the more organic it is.

Okay, now we do have cows only eating grass, and the question became "How do the grassarian cows get protein?"

I went online and search for the answers again. Yahoo answer gave me this page, and Baidu zhidao gave me this page. Basically they are saying that our stomach is not as good as the cows', and cows can even convert certain things in grass to protein.

Now I found the scientific answer, but I also want to mention the funniest answer which is:
"你真傻，牛B嘛"