Puzzle -- cattle disease grips bird (6)
I believe the answer is:
bemuse
'puzzle' is the definition.
(I've seen this in another clue)
'cattle disease grips bird' is the wordplay.
'cattle disease' becomes 'BSE' (bovine spongiform encephalopathy).
'grips' means one lot of letters goes inside another.
'bird' becomes 'emu' (emu is a type of bird).
'bse' going around 'emu' is 'BEMUSE'.
(Other definitions for bemuse that I've seen before include "Perplex" , "Nonplus" , "Muddle or stupefy" , "Puzzle and confuse" , "Bewilder or baffle" .)