At first, the animals work very hard in the belief that their work will benefit all, and are more satisfied with their labor because it is for the collective good. Some of the animals grumble because they are doing more work than their previous roles entailed, but overall they feel good about their work. Boxer becomes the hardest worker of all, often doing the work of two or more animals by himself; conversely, Mollie avoids the harder work as much as possible until she finally escapes the farm.
Every mouthful of food was an acute positive pleasure, now that it was truly their own food, produced by themselves and for themselves, not doled out to them by a grudging master.
However, as the pigs take power and keep the animals working harder, their joy slowly drains away. They work as hard as ever, but the rewards are smaller and the feeling is that they are no longer working for the good of all, but for the benefit of the pigs alone (although no animal dares speak that sentiment for fear of the dogs):
There was nothing with which they could compare their present lives: they had nothing to go upon except Squealer's lists of figures, which invariably demonstrated that everything was getting better and better.
(Orwell, Animal Farm, msxnet.org)
This is the end result of the experiment; they believe that their rebellion freed them from the cruelty of humanity, only to be taken over by the even crueler pigs. By the end, the animals are back to their previous status, only now the "masters" are the pigs, and instead of enslavement in ignorance, they force themselves to believe that they are enslaved for their own good.