In the book, Animal Farm, by George Orwell, what broke up the meeting?

The 'meeting' you refer to is the one called by Old Major, Mr Jones' prize white boar, at the beginning of the novel. He had had a strange dream the previous night and wanted to convey its message to all the animals, so decided to call a meeting as soon as Mr Jones was out of the way. It was to be held in the big barn. All the animals respected Old Major and were keen to hear what he had to say and quite willing to lose an hour's sleep to do so.

Before Old Major spoke about his dream, he wished to impart an important message which was quite clear: the animals were forcibly subjugated by Man's tyranny and were but slaves, manipulated and exploited because of Man's greed. Man was the animals' greatest enemy and they had to get rid of him to gain freedom and equality.

Old Major urged the animals to rebel against Man and once they were successful in this, to adopt seven maxims by which they were to live. This was to ensure that they did not adopt Man's corrupt habits and lived in prosperity and peace. Life without Man would be a nirvana for the animals.

Major then came to his dream and told them about a song which it reminded him of. It was a tune which had been taught as a child, which had become lost in memory, but was revived in the dream. The title was, 'Beasts of England' and it should become an anthem for their future rebellion and after. The song conveyed the idealistic state the animals would live in once Man was gone.

Once the lyrics had been grasped, the animals burst out into song in unison, each loudly singing the anthem in its own way. The commotion, however, woke Mr Jones who thought that there might be a fox in the yard.

He seized the gun which always stood in a corner of his bedroom, and let fly a charge of number 6 shot into the darkness. The pellets buried themselves in the wall of the barn and the meeting broke up hurriedly. Everyone fled to his own sleeping-place. The birds jumped on to their perches, the animals settled down in the straw, and the whole farm was asleep in a moment.

The meeting was therefore disturbed and broken up by Mr Jones firing his gun and, since the animals feared him, they all fled to their respective sleeping places and once they were settled down, quickly fell asleep. It was as if the meeting had never happened.