I believe the climax (or turning point) of Animal Farm comes when they send Boxer to the glue factory. Boxer was always the voice of hope among the animals with his phrases like, "I will work harder.", and "Napoleon is always right." He was also the hardest worker, who hoped that his work would be rewarded with a pleasant retirement after a lifetime of struggle.
However, when the other animals figure out that their leaders would not only deny Boxer his earned rest, but instead profited by selling him to his death...all hope seems to be lost.
SO, the denoument (or falling action), then, is after Boxer's death when the animals resign themselves to a terrible existance under the totalitarian rule of Napoleon. They know that no matter how hard they work, that the only end for all them is death.