Pipe animals up (4)
I believe the answer is:
reed
'pipe' is the definition.
(reed pipe is a kind of pipe)
'animals up' is the wordplay.
'animals' becomes 'deer' (type of animals).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'deer' written backwards gives 'REED'.
(Other definitions for reed that I've seen before include "Film director" , "Vibrating part of some instruments" , "Tall perennial grass" , "Tall water-loving grass" , "Grass of marshy land" .)