What is the most powerful agriculture ociation in America?

I'm writing a research paper for my political science cl, and the ignment was to choose an interest group and write about how it has effected laws ped or not ped on capitol hill. I'm interested in the meat industry. I was a vegan for three years, but have recently decided to eat meat from organic farmers whenever I can. I've seen the PETA videos and things are pretty nasty, but very few things seem to be done about the brutality and grotesqueness of slaughter houses. I'm curious to which interest group pushes the most pressure on politicians in this subject. It's due tomorrow and I'm a procrastinator, speedy responses would be encouraged. Thanks.