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.
Some scientists at Rockwell have genetically altered some cows to turn them into radioactive exploding zombie cows. Crypto and Pox discover this and destroy the scientists using their own exploding cows.
The government later acquired some radioactive cows to study at Area 42. This was a fatal mistake for the humans, as their explosive state has made Crypto's mission in weakening the base's defenses easier, then obliterate it using the Saucer.