Word of the rebellion on what is now Animal Farm spreads fast. We find this out in Chapter 4. But it does not result in total revolution on any of the other farms.
The way that the word is spread is through birds. Napoleon sends flights of pigeons out to other farms. The pigeons tell the animals there what has happened on Animal Farm.
The fact that animals on other farms do not rebel much comes mainly from the fact that humans try to play down the reports. The people spread rumors of horrible things that are happening on Animal Farm. They also punish animals who look like rebelling.