Well-organised old cow (4)
I believe the answer is:
neat
'cow' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for neat that I've seen before include "Taken without water" , "Bovine animal" , "Orderly, uncluttered" , "(Of alcohol) not diluted" , "Tidy and ordered" .)