Not even joking, this can actually be grammatically correct... Under the correct linguistic terms.
Our vocabulary for certain meats and their associated animals come from separate languages; English and French. The lower-class people who spoke English referred to the animals themselves, so they would say that they're eating pig, cow, deer, sheep, and so on. Meanwhile the French-speaking noblemen who didn't really need to deal with the live animals had words for them that would evolve into words like pork, beef, venison, mutton, etc.
So beef coming from beefs would basically mean "cow coming from cows".
In other words, saying that "beef comes from beefs, not cows" isn't really changing anything. You're still saying that you eat cow, you're just saying it in a more Romance vocabulary than Germanic... Isn't linguistics fun?
Also, fun truth, there is a tongue being born known as Anglish, which takes away the French and other tongue's words from English. It is lots of fun when making word-packs on the World Wide Web.