The victory is celebrated in true propagandistic style. The might of the animals are presented with the firing of guns. The wealth of the animals is celebrated with the food and the feasting. And, importantly, the wisdom of the leadership is celebrated with speeches and honors. 

This is all, of course, empty and odd because the project and hope of the whole farm is destroyed in the battle.

To the animals, the Windmill is symbolic of their freedom and independence.  It is a sign that they are doing a better job managing themselves that the humans did managing them.  So when the windmill is threatened, and when it is destroyed, it is a symbol of the animals’ failure and the failure of Animal Farm as a concept.

The sight of the demolished windmill spurs the animals to greater courage and after they run off the humans, they celebrate the victory with songs, speeches and the firing of the gun. But at least one animal, Boxer, questions the results. "What victory?" he asked, recognizing that his dead comrades and the destroyed windmill, of which he supplied most of the muscle, provided a hollow victory at best.

The turning point of the battle is when the dogs from Napoleon's bodyguard attacked the men from behind a hedge, outflanking them. This caused the men to run, but not without having inflicted terrible casualties on the animals. The animals celebrated with a speech by Napoleon as well as a funeral for the slain. Then there was a two day-long celebration that included songs, more speeches, and even an apple for every animal.