A lot of people think this is silly, and it is, but not for the reasons they think. The pork board has no choice; they are obligated to write these cease and desist letters, because of the way that trademark law is written in the United States.
A brand name or slogan is part of trademark law. People often confuse trademark and copyright, but they are not related. A trademark is a special case of a patent; trademarks are handled by the PTO, the Patent and Trademark Office of the government.
There's a provision in US trademark law that says that if you own a trademark, and someone else infringes the trademark in any way for any reason even for parody--copyright law protects parody, but trademark law does not), and you do not go after the infringer...Poof! You lose the trademark.
It doesn't matter who infringes the trademark, or how big they are, or for what purpose. If someone infringes and you don't go after them, your trademark is voided. If you want to keep the trademark, you have no choice but to go after every infringement, no matter how trivial or silly it is.
