It's a good point. I'm not an ag lawyer, but I am willing to bet that there's wiggle room in any grass-fed definition set by the USDA.

And you're right, there's also: plastic from water sources, plastic in the field that gets taken up by the gras, supplements given to the cow, plastic in the cutting board the meat was cut in, plastic the meat was wrapped in . . . it's hard to get plastic out of your supply chain.