Depending on who you ask, that stopped being the case the minute states started charging property tax. It's not yours, you just rent from the government. With the addition of zoning laws, it's hard to argue with that interpretation.

You can't sell a cow, put a 40 page long shrink-wrap license on the gate, and claim thus the milk or offspring are yours.

If Monsanto could prove the cow was GMO and their intellectual property, they could do almost exactly that. At the very least, they could put an injunction on the sale of cows and milk until they could verify if a patent had been broken. During which time, the farm would most likely go under.