Saying farm animals are behind the conclusion (7)

I believe the answer is:

epigram

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'saying' is the definition.
(I know that epigram is a type of saying)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for epigram that I've seen before include "Concise witty saying" , "Bon mot" , "Witty or sarcastic saying" , "witty comment" , "Gnome" .)

I've seen this clue in The Daily Express.

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