The cows one at least, is likely true. Cows are very curious and will tear into anything new. Especially any new box they find. Not a good idea to let them get up near your house, but not that uncommon either.
I once saw a cow take a big cow sized bite out of the brand new, exposed vinyl seats of a speed boat that was parked in the driveway. She didn't seem to like it, but she took a few more bites just in case.
I don't doubt that cows at their protein bars, but we were pretty far removed from that causality chain (Why were the cows near your mail? Why was FedEx leaving packages near cows?)
I once saw a cow take a big cow sized bite out of the brand new, exposed vinyl seats of a speed boat that was parked in the driveway. She didn't seem to like it, but she took a few more bites just in case.