The opening line of the chapter gives us an idea of this. It says, "All that year the animals worked like slaves. But they were happy in their work; they grudged no effort or sacrifice, well aware that everything that they did was for the benefit of themselves and those of their kind...".
Toward the early parts of the chapter, the animals seem willing enough to work harder to get their windmill built. Despite the lowering of rations and the increase in working hours, they maintain the state of mind that they are working now in order to make life easier in the future.
Then, when Napoleon plans to trade with humans, some of the animals are less confident. They remember that in the early days of the revolution, they had all agreed never to have any dealings with humans. They begin to doubt Napoleon's loyalty to the cause after this. Of course, they become more complacent when the dogs growl at them and Squealer convinces them they had never agreed to a ban on trade with humans in the first place. This same scenario plays out again when the pigs start sleeping in the beds in the farmhouse.
When the biggest setback of all happens and the windmill is destroyed, the animals are devastated. Of course, Napoleon's explanation that Snowball is to blame is readily accepted, and he urges them once again to continue their work.
Throughout the chapter, animals work grudgingly but willingly.