In Animal Farm, why is 'Beasts of England' abolished? In what way is the new anthem different from it? Why do the animals feel let down by it?

"Beasts of England" has unified and inspired the animals since before the Rebellion, but Napoleon abolishes it by decree. He has Squealer, his main propagandist, explain that the song is no longer needed because the dreams and ideals of the Rebellion that it expresses have already been achieved. The execution of the traitor animals earlier in the day completed the Rebellion, says Squealer. 

In fact, the song has become a threat to Napoleon's tyranny. The animals, not knowing how else to express their grief and disagreement with the execution, sing the song three times after the execution of the so-called traitor animals. It is a song of opposition and comfort that Napoleon wants stomped out, so he forbids it. Lyrics of "Beast of England," with five (one repeats, so there are six total) developed and different stanzas are full of imagery envisioning a better future. Here is one example:

Soon or late the day is coming, Tyrant Man shall be o’erthrown, And the fruitful fields of England Shall be trod by beasts alone.

Minimus's new anthem is much shorter, much simpler, and less filled with visions of a new order. It goes as follows: "Animal Farm, Animal Farm, Never through me shalt thou come to harm!"

The animals feel that neither the words nor the tune "come up to" the old "Beasts of England." They can't articulate exactly why, but a comparison of the rich, complex imagery and ideas of "Beasts of England," with its vision of a better, fairer, juster future for animals with the dull piece by Minimus shows that the second song does little to inspire or comfort the animals. This expresses a theme dear to Orwell's heart, that the dumbing down of language dumbs down thought and allows tyranny to flourish.