The animals had been convinced that their efforts would provide them with all of the things that Man had been had withheld from animals:
Only get rid of Man, and the produce of our labour would be our own. Almost overnight we could become rich and free. What then must we do? Why, work night and day, body and soul, for the overthrow of the human race!
Old Major told this to the animals in chapter 1 during his speech. They were motivated by the goal to get rid of man. With the destruction of man, the were consoled with the fact taht they could be free, wealthy, and that they could enjoy the fruit of their labor.
Throughout the rest of the book, the animals work and toil to create their own developed farm. Many of their efforts are more difficult and strenuous than they were when Mr. Jones was in charge, but it is the belief in freedom and eating the fruits of their own labor that encourages them.