What were the sacrifices that the animals had to build the windmill?

The animals work sixty-hour weeks all spring and summer in order to build the windmill, but none begrudges the extra labor. In August, Napoleon instates “strictly voluntary” labor on Sundays: animals may choose not to come, but they will have their rations reduced by half. There are plenty of building materials on the premises, and the animals discover that they can break limestone into pieces by using the force of gravity. However, the process of dragging boulders to the top of the quarry and throwing them down is very taxing. Boxer compensates by picking up the other animals’ slack, for which they admire him.