S19E17 Apocalypse Cow
Bart joins a young farmers' group for the summer and raises a cow he calls Lou, helped by local girl Mary. Appalled when he finds out that Lou is destined for the slaughter house, Bart, helped by Lisa, rescues him and takes him to Mary to look after. But Mary is the daughter of Cletus and Brandine and in yokel law the gift of a cow equals a marriage proposal. If Bart backs out Lou will die. Fortunately Marge comes up with a plan to save face and Lou but it's a close call for Homer in the pantomime cow outfit as he takes Lou's place on the way to the killing floor.