Some say a king is bovine (3)
I believe the answer is:
yak
'is bovine' is the definition.
(I have seen 'Himalayan bovine ' mean 'yak' so perhaps 'bovine' could also mean 'yak')
'some say a king' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'YAK' is hidden within 'say a king'.
(Other definitions for yak that I've seen before include "Tibetan beast; chatter" , "Tibetan animal" , "one sporting a thick coat" , "Hairy Tibetan ox" , "Long-haired ox of central Asia" .)