Bart and Lisa watch Saturday morning cartoons, starting with "Transclown-O-Morphs". The show's main character is quickly placed in a life-threatening situation and pleads with the viewers to help him survive by buying the new Transclown-O-Morphs cereal. Annoyed by the alleged commercial messages placed in every TV show the kids watch, Marge decides to get them away from the TV by having Lisa make banana bread and Bart go to Shelbyville with Homer to have the beanbag chairs "rebeaned". While Bart and Homer drive to Shelbyville, they see Martin Prince driving a combine harvester. Bart asks why someone like Martin would be driving a tractor, and Martin informs him he has joined 4-H. Lured by the prospect of operating heavy machinery, Bart joins as well and quickly masters driving a tractor. Later, the 4-H volunteer introduces the members to a competition. Taking them to the calf pen, he informs them that they will each pick a calf and raise it over the summer, at the end of which the cattle will be judged at the county fair.
Bart is stuck with the runt of the litter, and is unable to trade it away. He soon meets Mary, and she encourages Bart not to give up in the competition. Bart agrees, and they rename the young bull Lou (previously Lulubelle). Throughout the following weeks, Bart takes good care of Lou and helps him become stronger, while also bonding with him and growing to love him. When the day of the competition arrives, Lou has matured into a large bull and is awarded the blue ribbon. Bart is ecstatic until Lisa informs him that the next step is to send Lou to a slaughterhouse.
Bart tries to convince Marge and Homer to buy the bull, but knowing by experience how expensive it is to care for a large animal, they refuse. That night, Bart hears mooing as he lies in bed and believes it to be a hallucination caused by his inability to help Lou. He starts yelling in fear, and Lisa arrives and says it is simply his subconscious telling him to stop eating meat. However, the mooing is suddenly replaced by clucking noises, and Bart discovers that it was only a CD of Tress MacNeille's "Anguished Animals III," placed by Lisa, in an attempt to turn him vegetarian. Nevertheless, Bart, Lisa, and Lisa's friends, "Compost" and "Solar Panel", go to the slaughterhouse in the middle of the night, determined to save Lou. They discover that Lou, who has been fed growth hormones, is now much bigger, so they use a forklift to pick him up and carry him away (though not without some trial and error). Hurrying from the slaughterhouse, they decide the only safe place they can take him is to Mary's home, which is on a farm. The next morning, they're surprised to see that Mary is the daughter of Cletus Spuckler.
Bart gives the cow to Mary, and Mary agrees to take it. Cletus then yells for Brandine to come to the door. When Brandine learns that Bart offered Mary the cow, she informs them that the giving of a cow constitutes a formal proposal of arranged marriage. Against the wishes of both Bart and Mary, Cletus and Brandine plan the wedding for the next day; Lisa convinces Bart to go along with it long enough to let them figure out a way to save Lou, correctly suspecting that Cletus will not keep the bull if Bart refuses. Upon learning what has happened, Homer and Marge are shocked, and Marge devises a scheme to prevent it, but she also agrees to save Lou, knowing how Bart rarely cares about anyone or anything. The next day, Marge arrives to stop the wedding, prompting Cletus to send Lou to the slaughterhouse. However, the "Lou" Cletus sent was actually Homer in disguise, while the real Lou is being sent to India to be treated like a god. They save Homer from the slaughterhouse after a close shave, after which Homer vows to cut back on his meat eating, and Bart reflects with pride that he can finally say that, "I had a cow, man."