Who taught the animals a song and what was the song?

In the opening chapter of the novel "Animal Farm" Old Major addresses all the animals on the farm:

"Many years ago, when I was a little pig, my mother and the other sows used to sing an old song of which they knew only the tune and  the first three words. I had known that tune in my infancy, but it had long since passed out of my mind. Last night, however, it came back to me in my dream. And what is more, the words of the song also came back-words, I am certain, which were sung by the animals of long ago and have been lost to memory for generations. I will sing you that song now, comrades. I am old and my voice is hoarse, but when I have taught you the tune, you can sing it better for yourselves. It is called 'Beasts of England'."

Old Major cleared his throat and began to sing. As he had said, his voice was hoarse, but he sang well enough, and it was a stirring tune, something between 'Clementine' and 'La Cucaracha'."

So the song "Beasts of England" was taught to the animals on the farm by Old Major.

However, in Ch.VII Napoleon abolishes the "Beasts of England," and,

"In its place Minimus, the poet, had composed another song which began:
'Animal Farm, Animal Farm,
Never through me shalt thou come to harm!'
and this was sung every Sunday morning after the hoisting of the flag. But somehow neither the words nor the tune ever seemed to the animals to come up to 'Beasts of England'."

Moreover, in Ch.VIII as Napoleon becomes all powerful Minimus once again composes another poem. This poem is nothing but an anthem to flatter Napoleon, the second stanza of which goes like this:

"Thou are the giver of
All that thy creatures love,
Full belly twice a day, clean straw to roll upon;
Every beast great or small
Sleeps at peace in his stall,
Thou watchest over all,
Comrade Napoleon!"