Old Major's dream envisioned an earth of the future with no humans, where animals ruled the world and determined their own actions. He pointed out that all of the evil in the world was the result of humanity, and declared that the animals should all maintain an "enmity" toward humans. The animals should avoid all human characteristics, even after they have been conquered. By the end of the novel, at least one part of Old Major's dream had come true: The leaders of Animal Farm were considered equals among their new human associates, but the pigs had broken nearly every commandment in the process, from wearing clothes to walking upright. The other animals were now worse off than they had been under their human masters, working longer hours for less sustenance. The animals were all equal, but some were just more equal than others.
Old Major saw the world without humans, with animals working and providing for themselves.
The end is ironic in this context because the animails are indeed working, but it is merely for other animals. They toil and sweat to provide for those animals who have seized power.
Old Major could never have known how the animals (the pigs) would pervert his dream.