Farm animal eats hot dog (4)
I believe the answer is:
chow
'dog' is the definition.
(chow is a kind of dog)
'farm animal eats hot' is the wordplay.
'farm animal' becomes 'cow' (I've seen this before).
'eats' means one lot of letters goes inside another.
'hot' becomes 'h'.
'cow' enclosing 'h' is 'CHOW'.
(Other definitions for chow that I've seen before include "Dog (from China?)" , "Barker" , "[HOUND]" , "Food (colloq.)" , "breakfast?" .)