What ideology does Old Major talk about to the farm animals?

What becomes known in the book as animalism bases its ideas on Marxism. Like Marxism, animalism aims to liberate the workers from their oppressors, which in this case are the farmers.
As Old Major states, the animals live their lives for the benefit of others, not for themselves.

No animal in England is free. The life of an animal is misery and slavery: that is the plain truth.

His arguments are based on some undeniable truths. “Man,” he states, “is the only creature that consumes without producing.” Humans rely on the animals, or workers in the case of Marxism, to survive. Yet it is man who lords over the animals. If the animals would unite and “get rid of man,” then they would have complete control over the produce of their own labor. “Almost overnight we could become rich and free.”
Like Marxism, animalism only really works if everybody is equal—that is, everyone must have equal wages and equal chances of success. Unfortunately, as what happened in Communism, it doesn't work out that way. The pigs, becoming increasingly powerful, eventually change the rules of animalism to benefit themselves.

The ideology that Old Major lays out to the other animals is classic Marxism. He tells the animals that their labor produces all the wealth of the farm. But, he says, Mr. Jones takes the profits for his own benefit. He lives a comfortable life with plenty to eat while the animals toil hard, live in rough, unheated stalls, are whipped, and get barely enough food to eat. At the end of their useful lives, the animals get no retirement but instead are sold to the glue factory or otherwise killed.
Old Major explains that this is unfair. People like Farmer Jones, he says, are essentially useless. Old Major describes a golden future in which the animals will eventually rise up and take over the farm, running off the humans. The animals will then manage the farm themselves. Because they will keep all the profits from their labor and share the wealth among themselves, they will live prosperous and joyful lives.