It's the Old West and prize-winning heifer Maggie (voice of ROSEANNE BARR) is the lone cow left on the Dixon farm after cattle rustler Alameda Slim (voice of RANDY QUAID) and his three dimwitted nephews, Phil, Bill & Gil Willie (voice of SAM LEVINE), have done their dirty work.
With the farm up on the auction block, Maggie is sent to live on the Patch of Heaven dairy farm run by Pearl (voice of CAROLE COOK) and Mrs. Caloway (voice of JUDI DENCH), the stately and matronly lead cow. The latter isn't happy to welcome Maggie to their fold that includes fellow cow Grace (voice of JENNIFER TILLY), ornery goat Jeb (voice of JOE FLAHERTY), Ollie the pig (voice of CHARLES DELL) and flustered chicken Audrey (voice of ESTELLE HARRIS).
Things only get worse when Sheriff Brown (voice of RICHARD RIEHLE) arrives on the scene and informs Pearl that if she doesn't come up with the money she owes the bank, her farm will also face foreclosure. Since Pearl won't sell any of her animals, she sees no solution.
Upon hearing that the reward money for the capture of Slim equals the amount owed, Maggie, on the other hand, decides that they should set out and nab the cattle rustler. Mrs. Caloway thinks it's crazy, but Grace is up for that and Caloway eventually but reluctantly joins them on their quest.
They're not alone, however, in their desire to capture Slim. There's legendary bounty hunter Rico (voice of CHARLES DENNIS) who borrows the sheriff's horse, Buck (voice of CUBA GOODING, JR.), for his ride and then decides he's not right for the job. Accordingly, the steed sets out on his own to get Slim.
From that point on, and with the aid of the peg-legged jackrabbit Lucky Jack (voice of CHARLES HAID), the bovine trio tries to find and capture Slim before anyone else does or before the rustler sells his stolen herd to the likes of cattle buyer Wesley (voice of STEVE BUSCEMI).