Here are a couple of links. The basics are that animals, like humans, have moral status and thus we are not justified in unnecessarily bring harm to them through practices like egg farming and cattle farming. Cargill's agriculture practices are a far far far way from the ideal farming scenarios described in the common "Happy Cows" argument. It's pretty clear that even if their meat wasn't poisoning people, their production of it would still be immoral.
https://plato.stanford.edu/entries/moral-animal/
https://www.reddit.com/r/AskPhilosophyFAQ/comments/4i0iqx/wh...