Pig

A pig is a four-legged animal native to Earth.

References to Pigs
In 1930s New York, the Cult of Skaro turned the less intelligent into Pig slaves (DW: Daleks in Manhattan/Evolution of the Daleks)

In 2006, a pig was augmented by the Slitheen as a hoax alien invader. (DW: Aliens of London)

By year 5000 some cyborgs used the brain of a pig, Mr. Sin was one such cyborg from this period. (DW: The Talons of Weng-Chiang)