How does Old Major use persuasive language in his speech to the other farm animals in Animal Farm by George Orwell?

Old Major, a boar, is a persuasive speaker. He tells the other animals he is going to describe a dream he had last night, and describes a dream of a better future for the animals. Many of the animals are not very intelligent, so Old Major's ability to state a simple solution in simple words is persuasive: their problems are all due to mankind. This is easy for the animals to grasp and Old Major lays out the reasons why mankind is to blame: men force animals to work to "the last atom" of their strength and then send them out to a "hideous" slaughter. Words like "hideous," "last atom," and "miserable" depict the animals' lives in the worst possible terms. The animals work by laying eggs, giving milk, and tilling the fields, but humans collect all the profits. Old Major uses heightened language to describe the behavior of men; Old Major claims that men don't just take some of the milk, but all of it, so "Every drop of it has gone down the throats of our enemies." Of course, it's probable that the baby calves get some small part of the milk, but Old Major exaggerates for effect. This kind of language is meant to arouse and inflame the emotions of the animals and to cause them to feel deprived of their rights.  

Old Major then draws a contrast between the hard life the animals currently experience and the good life they could have without mankind. Using heightened language, he describes this good life as "a comfort and a dignity beyond imagining." Meanwhile, the animals, such as the porkers, "scream your life out at the block." The starkness of the contrast helps persuade the animals that man is the enemy and the animals should rebel when the chance arises. In fact, he ends on that black and white note: man is the "enemy," and all animals are friends. Old Major's language allows for no nuance, no possibility that any human anywhere could be anything other than an enemy.

Vivid, heightened connotative language that puts the animals' current lives in the worst possible light, simple solutions stated in simple terms, and the use of contrasts between an imagined future and the harsh reality of the present all help Old Major persuade the animals to be ready for rebellion.