There are of course a number of things that are abolished throughout this famous allegory. Of course, the first thing to go is the human rule, as the animals launch their rebellion and dispense with humans altogether. However, apart from the obvious things that are abolished, such as "The Beasts of England," we can equally point to other more important and more insidious changes that have occurred in the animals existence.
By far the most important of these is the way that truth and honesty have been dispensed with. Thanks to the efforts of Squealer, it is clear that the reasons and motives for the changes that are made and the things that are abolished are cloaked and left hidden from the rest of the farm animals. Perhaps this can most clearly be seen in the way that the Seven Commandments gradually become whittled down bit by bit, until finally it only includes the following sentence:
All animals are equal, but some animals are more equal than others.
The way in which these changes are brought in show the way that freedom of thought and being able to speak your mind are abolished bit by bit, thanks to the manipulation and deceit of the pigs.
I think that this answer could be taken on both a literal and symbolic level. At the end of the book, Napoleon, not one for big speeches, launches into a big speech about the changes he has made to the farm. The use of the term "comrade" has been abolished. This is an example of how language use relates to power. The animals no longer recognize equality in their speech. This underscores the abolition of equality amongst the animals, something that was present in the days following the revolution. Another element that has been abolished has been the name of "Animal Farm." The farm becomes renamed "Manor Farm." The significance of this is that this was the name of the farm under Jones, indicating that the force the replaced him has actually become him. In a symbolic manner, the spirit of Animalism that was preached in the beginning by Old Major before his death has also been abolished. The pigs' assumption and consolidation of power has been one where Old Major's vision of harmonious coalescing of power amongst the animals has been replaced by a structure whereby the pigs and dogs represent the humans controlling other animals. The abolition of the spirit of public exchange, evident in the Sunday morning meetings, has served to highlight how Napoleon and the pigs represents so much that is fundamentally different from what Old Major sought to bring to the animals with his vision of Animalism in the opening chapter.