Winston is a prize pig that Crow T. Robot and Tom Servo were keeping in The Satellite of Love's feedlot, as of experiment 1012. This was all news to Mike Nelson, as he was unaware that there was a feedlot (or a silo for Winston's silage) on the SoL.
Crow and Tom raised Winston from an eight pound piglet and, at the time of Pearl's "Fair", he weighed 5,743 pounds.