It is interesting to look at the efforts of Old Major to use persuasive techniques.
He uses the rhetorical question: "You cows that I see before me, how many thousands of gallons of milk have you given during the last year?"
He uses the emotional persuasive appeal of fear: "You young porkers... every one of you will scream your lives out at the block within a year. To that horror we must all come -"
He uses the logical persuasive appeal by expressing to animals they do all the work, the humans profit from it.
He uses the charged words "comrade" and "Rebellion!" Each of these has connotation. A comrade is a friend, uniting all animals with an equal part in this process. Rebellion is a strong act and thus has an emotional charge. Rebellion in this regard cannot be done alone, but must be done as a group.
Throughout the speech you see other instances of propaganda and persuasion... stereo-typing, slogan, authority (he establishes himself as an older more credible judge than the rest).
My first impression of the speech is that it makes a lot of sense as long as you accept the basic premise that the animals are intelligent beings. It is clear that the animals are being oppressed and it is clear that it is the people that are doing it.
What is less clear is that getting rid of the people will solve everything. It would take away that particular oppressor, but true equality will require that the animals will not have the same ambitions that people do. Old Major assumes that they will not. He assumes they will live in harmony. But that is just an assumption and it turns out to be wrong.