How possible is a system like IBP today?

In Chapter 7, Schlosser mainly discusses the overwhelming effect the trust of the Iowa Beef Packers had on the meat packing industry. The IBP gained control over a lot of the industry in North America and became almost monopolistic, to the point of having to be broken up with antitrust laws. I know this happened a few decades ago, but I was wondering if any kind of control is available to an entrepreneur willing to seize power over a certain industry in the US today, specifically with food. I know there are some companies like Luxottica that seemingly own all the products on the market, but is this also considered a monopoly? Also, how would it be determined by today's standards and how has that changed since the Supreme Court's decision about IBP?