The film, especially the ending, doesn't follow the book closely. (See: Epilogue).
Following the return of a drunken Mr. Jones to Manor Farm, the pig Old Major calls a meeting of all the animals. He tells them to revolt against Jones and to take control of the farm for themselves, calling for a life of equality and prosperity. Following his death that night, the animals break into the food stores; Jones overhears the animals and comes in whipping his whip in every direction. The animals rebel against Jones and run him off the farm. Soon the animals repel a human counterattack, and the two pigs Napoleon and Snowball assume command of the animals, singing a revolutionary song as they burn his harnesses and whips.
The farm prospers under the animals. Snowball promises the other animals a better future through hard work. Napoleon drives him away from the farm with a bunch of orphaned dogs he raised harshly, denouncing him as a traitor, and presents Snowball's plan for a windmill as his own, taking charge of the farm and deputizes another pig, Squealer.
There is little food available to the other animals, but the pigs have plenty. Boxer the horse and his friend Benjamin the donkey work long hours helping to build the windmill, and later discover the pigs sleeping in beds in Jones' house; the commandment against beds has been changed on the barn accordingly. The farm, under Napoleon's leadership, begins to trade with the outside world, represented by Mr. Whimper. Squealer tells the chickens that their eggs will be taken as trade goods, contradicting what they were told by Old Major. They attempt to revolt but are caught by the pigs. In a scene reminiscent of Stalin's purges, the chickens (along with a sheep and a goose that was seen earlier in the film as a gosling) confess their 'crimes' and are killed off-screen by the dogs. The animals' blood is used to edit one of the commandments.
The revolutionary song is then forbidden by Napoleon under the penalty of death, and trade continues. The other farmers become jealous of Whimper and attempt to seize Animal Farm. A battle ensues during which Boxer is shot in the leg, and from which the animals emerge triumphant. In the meantime, however, Jones blows up the windmill (and obviously himself, as he is in a drunken stupor at that time and he isn't seen escaping from the mill and doesn't appear in the rest of the film). During the winter, the animals rebuild the windmill whilst the pigs languish in the farmhouse. Boxer's health deteriorates until one night, when he collapses during a storm. A van, apparently an ambulance, arrives to take Boxer away, but turns out to be from Whimper's glue factory, with the pigs receiving a case of whiskey in payment, and Squealer delivers a phony speech. The animals realize that the pigs have betrayed the revolution and used it for their own ends, but are stopped from doing anything by the dogs.
Years later, Napoleon's schemes have proven so successful that other farms (under their pig leaders) have joined his cause. During a meeting of the pigs, Benjamin the donkey discovers that they intend to suck the other animals completely dry with even more work and less food. Now at the end of his patience and ready to take his chances with another revolt, Benjamin stirs and leads a multi-farm revolution against Napoleon and his cohorts. The dogs are too drunk to fight, and Napoleon and the other pig leaders are presumably killed when the house is destroyed with them inside it, ending the dictatorship.
- In the novel, Old Major calls for the eventual overthrow of humanity as a whole, and blames all of man for animal-kind's woes. In the film, his speech seems to directed purely at overthrowing Mr. Jones and Manor Farm, and he does not call for nor even imply the spreading the revolution outside of Manor Farm. Instead, it is Snowball who brings up the idea of spreading the revolution to the other farms after the first harvest after the revolution, with mixed results.
- Additionally, at the end of the novel, Napoleon says that he does not wish to expand animal (or rather, pig) rule beyond Animal Farm to his human guests. In the Film, it is not only seen that he wishes to, but has actually done so.
- The vote of whether or not rats and other wild animals are considered comrades never takes place in the film. In addition, there is no effort made towards bringing the wild animals into the fold.
- In the film, Mr. Jones runs the farm alone. In the novel, he's accompanied by at least 4 other men and his wife, whom is also absent in the film.
- Benjamin is portrayed differently in this film than he is in the novel. He still is a donkey, but is portrayed as the film's protagonist. Years after Boxer's death, Benjamin discovers Napoleon's evil plot to completely overwork the animals, and leads the animals during the 2nd revolution. In his young age, he also works together with Boxer when he works late hours. In the novel, this never occurs.
- Boxer is nonchalant, in the film.
- In this film Mr Whymper is a salesman who starts trading with the pigs. He also owns the glue factory to which Boxer is sent.
- The windmill was only destroyed once in the film, by Mr Jones. In the novel, it was destroyed twice, once due to poor construction (though it was blamed on snowball), and once by a human raiding party in the Battle of the Windmill
- The cat has a lesser role in the film.
- The puppies that grew to be Napoleon's bodyguards were not taken away from their mother. Instead, Napoleon quietly stole them away to raise them after their mother was killed.
- In the film, the animals realize the pigs' true aims in Boxer's death.
- In the film, the cat is killed by two of Napoleon's dogs when they were hunting the hens. In the novel, she remains alive.
- Snowball ran away and was never seen again in the novel, with no information provided on his ultimate fate after the novel. In the film, he was killed by Napoleon's dogs when they pursued, though this is kept from the other animals.
- Old Major dies immediately after telling the animals about his dream while in the novel he lives for three more nights. (Additionally, in the film, it is the animals' sorrowful reaction to Old Major's sudden death that wakes Mr. Jones up; in the novel, it was the singing of their anthem that woke Jones up)
- There are only five Commandments in this film. In the Novel, there were Seven Commandments. Commandments 1 and 2 from the novel are condensed into a single commandment: "Four legs good, two legs bad", and Commandment 3 is cut out altogether.
- In the novel the pigs make a habit of trading with humans when they need building materials and other things that are not available on the farm. In this film, they start trading with Mr. Whymper when Napoleon runs out of jams and jellies that were left behind when Mr. Jones was expelled.
- Mr. Frederick and Mr. Pilkington's roles are reduced, and they are never mentioned by name.
- At the end of the film, Benjamin sees the pigs 'transform' into Jones by his hallucinations.
- Clover and Muriel don't have much of a part in the film as they do in the book, and are never mentioned by name.
- Jones did not participate in the Battle of the Windmill in the novel. In the film, he single-handedly destroys it just after all the other humans have been driven off.
- Snowball's plans for the windmill were never shown to the animals and Napoleon later said that they were his plans when first unveiled.
- "Four legs good, two legs bad" is only used twice in the film (although it is uttered by the sheep on at least five occasions). Additionally, "Four legs good, two legs better!" heard near the end of the novel by the sheep, is never used in the film.
- Napoleon's favorite sow never appeared.
- The term "Animalism" is never used. Neither is the flag representing it.
- Mollie is not in the film. In the book, she is a slightly important character until she leaves to be with humans.
- In the end of the film the card game where Pilkington and Napoleon both draw the ace of spades never happens.
- Also in the end of the novel, humans from other farms (specifically, Pilkington) are meeting with Napoleon. In the Film, it is pig rulers he is meeting with from "farms run by pigs", implying that pigs have taken over other farms, or have formed farms of their own, or both (Implying the Domino theory at work). This was never implied to have happened in the novel.
- The renaming of Animal Farm back to Manor Farm never happens in the film.
to realise that the pigs have become nothing better than the human masters of old.
In a stark departure from Orwell's book, the film ends immediately after this iconic image with the animals revolting against the pigs. John Halas, one half of the directing team, later reflected that the film needed the happier ending of counter-revolution, as it rewarded the audience for their emotional investment.
The animation historian Brian Sibley doubts that the team responsible was aware of the source of the funding, which is now accepted to have come from the Central Intelligence Agency, whose concern was to facilitate the creation of anti-communist art.
Much of the pre-release promotion for the film in the UK focused on it being a British film instead of a product of the Hollywood studios. The film critic C. A. Lejeune wrote at the time: "I salute "Animal Farm" as a fine piece of work… [the production team] have made a film for the eye, ear, heart and mind". Matyas Seiber's score and Maurice Denham's vocal talents have been praised specifically (Denham provided every voice and animal noise in the film). The animation style has been described as "Disney-turned-serious".
Some criticism was levelled at the altered ending, with one paper reporting: "Orwell would not have liked this one change, with its substitution of commonplace propaganda for his own reticent, melancholy satire".
To coincide with the film's release, a comic strip version was serialised in newspapers, drawn by Harold Whitaker, one of the animators. Scenes from Animal Farm, along with the 1954 adaptation of Nineteen Eighty-Four, were featured in "The Two Winstons", the final episode of Simon Schama's program A History of Britain.
When first released, the British Board of Film Classification gave this film a rating certificate of "X" (the same category is now "18") prohibiting anyone under 18 from seeing the film, presumably due to its very political and violent behaviour. The film has since been re-classified as "U" (Universal), suitable for all audiences.
In 2000, The New York Times printed an article alleging that the CIA had been covertly involved in the purchase of the film rights from Orwell's widow. They subsequently went on to modify the screenplay from the original novel to overemphasize the anti-communist byline of the original story.
The CIA's funding and deep editorial involvement in the film is demonstrated and thoroughly examined in Daniel Leab's 2007 book Orwell Subverted: The CIA and the Filming of Animal Farm (2007; Pennsylvania State University Press). The CIA continues to decline Freedom of Information Act requests concerning the film.
The 'Special Edition' DVD includes a documentary hosted by television actor and popular historian Tony Robinson.
- After the first battle, the color of the puppies changes between shots - cream-ivory colored when we first see them, grey when Napoleon takes them up into the barn.
- As the film goes on the pigs alter the writing on the side of barn; the first being the addition of 'sleep in a bed with sheets'. Later on this and other additions are not present.