Cows are animals found on Earth.
Crypto first encounters cows at Turnipseed Farm. Pox assumes them to be the dominant lifeforms on the planet. They try to communicate with them, but it proved to be pointless. Crypto then uses PK to hurl the bovines into oblivion.
The scientists at Rockwell have genetically altered some cows to make them radioactive and explosive. Crypto and Pox discover this and destroy the scientists using their own exploding cows. The government later got some radioactive cows for study at Area 42. This proved to be a major error for them, as Crypto used these to destroy the base's defenses, then obliterate it using the Saucer.