Tsar’s egg addled, leading to complaint (8)
I believe the answer is:
staggers
'complaint' is the definition.
(medical complaint in farm animals)
'tsar's egg addled' is the wordplay.
'addled' is an anagram indicator.
'tsars'+'egg'='tsarsegg'
'tsarsegg' is an anagram of 'STAGGERS'.
'leading to' is the link.
(Other definitions for staggers that I've seen before include "is shocking" , "causes amazement" , "Disease on farm" , "is astonishing" , "Reels about like gagsters" .)