The Simpsons - Episode 19.17 - Apocalypse Cow

Thanks to DV30302 for the following.

When Bart joins the 4-H Club, he unexpectedly falls in love with a cow named Lou. But when Bart finds out that Lou has been sold to a slaughterhouse, he becomes determined to save him. Bart and Lisa free Lou from the slaughterhouse, and Bart gives the cow to Mary, a fellow 4-H Club member.

"However, Mary's father mistakenly believes Bart is giving them the cow as a dowry for Mary's hand in marriage. When Homer and Marge hear of Bart's engagement, they devise a plan to save Lou and free Bart from his marriage.

Source: Fox