Top cow (6)
I believe the answer is:
jersey
This clue could be a double definition.
'top' is the first definition.
(item of clothing)
'cow' is the second definition.
The answer and definition can be both animals as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
Can you help me to learn more?
(Other definitions for jersey that I've seen before include "Channel land < top" , "Milked" , "Knitted garment" , "Warm garment or Channel Island" , "farm animal" .)