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.