Foxy Makes Me Happy

"Lady, Play Your Mandolin!" from 1931

From WikiPedia:

Lady, Play Your Mandolin! was the first Warner Bros. Merrie Melodies cartoon, directed by Rudolf Ising of Harman and Ising. It was originally released in August 1931.

As was typically the case with the early entries in the Merrie Melodies series, one purpose of the cartoon was to promote a Warner-owned popular song. The title theme, written by Oscar Levant with lyrics by Irving Caesar, was a 1930 #5 pop hit sung by Nick Lucas and released by Brunswick Records, which had been purchased by Warner Brothers the previous year (Another recording, by the Havana Novelty Orchestra was released the same year on RCA's Victor Records). In the short, it is sung by a female fox character who would later become Foxy's girlfriend, Roxy.

The short was animated by Rollin Hamilton and Norm Blackburn with a musical score and direction of the Brunswick Recording Orchestra by Frank Marsales.