Cash Cow

The Cash Cow was a large creature used for illegal meat production near Cardiff on Earth in 2008. It was believed to have been taken from the sea when it was small, but due to a mutation which caused it to constantly grow it soon reached a massive size and nearly filled up the warehouse it was kept in. This mutation allowed the producers to harvest meat from it while it was still alive, as it would just grow back.

It was killed by Owen Harper of Torchwood 3 when the team raided the building to find the origin of the meat. The keepers of the Cash Cow believed it was a non-sentient Terran creature from the depths of the ocean; however, Jack Harkness believed that it was not from Mutter's Spiral at all. (TW: Meat)

Behind the Scenes
The cash cow bears a resemblance to the "Chicken Little" creature in the novel "The Space Merchants" by Frederik Pohl and Cyril M. Kornbluth. However, "Chicken Little" was not sentient.