Innards of farm animals, livestock primarily (5)
I believe the answer is:
offal
'innards' is the definition.
(I have seen 'Edible innards' mean 'offal' so perhaps 'innards' could also mean 'offal')
'of farm animals livestock primarily' is the wordplay.
'primarily' indicates taking the first letters.
The first letters of 'farm animals livestock' is 'fal'.
'of'+'fal'='OFFAL'
(Other definitions for offal that I've seen before include "Edible (or inedible?) internal organs" , "Edible (or inedible!) animal organs" , "Lights perhaps" , "Bits of waste meat" , "Liver, kidneys etc - rubbish" .)