Old Major’s speech inspires the animals to strive for a better existence. How do the promises of this dream differ from the reality of their lives under Napoleon?

Old Major paints a picture of the better life the animals will have when they take over the farm and run it for their own benefit. After the animals revolt, he says, which might happen in their own lifetimes, or might be after they die, the lives of all animals will be much improved.
The animals, Old Major says, are miserable and exploited because of humans. In the song he teaches them, "Beasts of England," he describes what their new lives will be like after they drive off the humans. The animals will no longer wear bits or harnesses or be beaten with whips. They will have an abundance of food. They will have "riches."
Old Major also depicts a life in which animals will be able to retire in old age, have more than bare stalls to sleep in, and be able to enjoy leisure time rather than merely toil from dawn to dusk.
After Napoleon takes over, however, the animals end up worse than when they worked under Farmer Jones. Boxer, for example, after years of dedicated labor above and beyond the call of duty, gets no retirement. Instead, he is sold to the glue factory to be killed. The animals, except for the pigs and dogs, toil hard and are often hungry. Their stalls stay bare, and they never get the heat and electricity that was once promised.
The pigs, on the other hand, live in Farmer Jones's old house, wear clothes, sleep in beds (all things Old Major said animals should never do), and even carry whips to oppress the other animals. The dream of a good life and solidarity for all animals has been destroyed. At the end of the book, a delegation of human farmers come to visit Animal Farm, and we learn they are impressed with how it is run. As Mr. Pilkington states, the other farmers have found

a discipline and an orderliness which should be an example to all farmers everywhere. He believed that he was right in saying that the lower animals on Animal Farm did more work and received less food than any animals in the county. Indeed, he and his fellow-visitors today had observed many features which they intended to introduce on their own farms immediately.