George Orwell's - Animal Farm (1954)

Animal Farm is a 1954 British-American animated comedy-drama film produced by Halas and Batchelor, based on the book Animal Farm by George Orwell. It was the first British animated feature (Water for Firefighting and Handling Ships, two feature length wartime training films, were produced earlier, but did not receive a formal cinema release). The US CIA paid for the filming, part of the American cultural offensive during the Cold War, and influenced how Orwell's ideas were to be presented. The CIA initially funded Louis de Rochemont to begin work on a film version of Orwell's work and he hired Halas & Batchelor, an animation firm in London that had made propaganda films for the British government.

Maurice Denham provided the voice for all the animals and as well as humans in the film.

https://en.wikipedia.org/wiki/Animal_Farm
https://en.wikipedia.org/wiki/Animal_Farm_(1954_film)

As this is more then 50 years old I assume that copyright is no longer an issue.