Bill Thompson voices various characters in the film, including: Jock the Scottish terrier, Bull the English bulldog, Dachshie the German Dachshund, the policeman outside the zoo and plenty more. This wasnottheonly Disney animated feature he appeared in, either.
Fred Flintstone as Boris the Russian Wolfhound philosopher at the dog pound.
Mandy Moore voices Lady in some later installments of the franchise.
Screwed by the Lawyers: Peggy Lee sued Disney when the movie debuted on home video under the Walt Disney Classics label in 1987, citing that her contract did not allow them to use her voice on video. She eventually collected a seven figure sum, and Disney began including in their contracts rights to "media not yet existing."
Talking to Himself: Peggy Lee, Dallas McKennon, Lee Millar and Bill Thompson each perform more than one role in the film.
Ur-Example: This was the first animated feature screened in Cinemascope, the first Disney animated feature to be distributed under Buena Vista Distribution (as opposed to RKO Radio Pictures, as previous ones had) and also one of the first animated Disney films to be (mostly) based on an original story by Joe Grant.
The casting of Peggy Lee as voice actor and songwriter was also one of the earliest examples of a "big name" in an animated feature at the time.
What Could Have Been: Trusty was supposed to die after the dogcatcher's wagon hit him, but Walt Disney didn't want another serious death, following the trauma Bambi's mom's demise caused many children.
Boris the Russian Wolfhound (who appears at the pound) was originally supposed to be the male lead of the film, having Tramp's role. However, the title "Lady and Boris"..."just didn't have the right ring to it".
Tramp/Boris was also supposed to have had a song, called "I'm Free as the Breeze", which he sang about his life as a happy stray. It was cut when the film was retooled.
In one early version, the rat spoke and was more of a troublemaker than a genuine menace. He would have had a Jersey gangster sort of personality.