The corn consumed by cattle includes the corn stalks which are more or less the same as consuming grass. Corn is after all in the grass family. The actual kernels of corn increase the calories versus grass, but it’s not like cows are just eating corn off the cob all day long. They need to consume tons of roughage to help with their digestion. I think a good argument is that converting grain and grass to beef is inefficient - if you could have consumed the grain yourself, but the nice thing about cows is that they convert very low calorie foods into high calorie meat that we can consume. If we had to eat what cows do, we’d be chewing all day.
It is well documented that once cows are switched to the pure corn diets we now feed them, their health starts immediately declining and they start dying. Factory farms time it so that they grow up on grass and similar, then are switched to grain to fatten them, and are slaughtered before becoming too ill. There are many unhealthy modifications made to their diet and environment to force them to consume corn. This is detailed lots of places including the book The Omnivores Dilemma. The whole book is essentially about corn and what a horror show industrial agriculture/meat is.
Yes. Large parts of North and Central India eat wheat a lot, as chapati, roti, paratha, naan, bhatoora, poori, daliya (broken wheat), rava (semolina), etc. Even in South India a good amount of wheat is eaten as rava (rava upma and rava dosai), chapati, poori, parotta, etc.
Same for monocrop fields of Soy beans, doused in pesticides & chemical fertiliser.
There is a better way all around, with a mixture of animals and crops. And you very much need the animal dung to fertilise if we're talking about doing anything postive for the environment.
They don't get silage unless the farmer makes a point of it. Most of the time the stalks and chaff and spit out the back of the combine and tilled under. Furthermore they'd get penalized for it in weighing if its mixed in with the corn so there's little to no incentive for the extra work of it. If the farmer has a small enough herd though they may let them roam on the field afterward, but the big lots don't do that.
