In zooming up, you get low! (3)
I believe the answer is:
moo
'low' is the definition.
(both can mean to make the noise of a cow)
'in zooming up' is the wordplay.
'in' says the answer is hidden in the clue.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'oom' is hidden within 'zooming'.
'oom' reversed gives 'MOO'.
'you get' acts as a link.
(Other definitions for moo that I've seen before include "Farmyard sound" , "Cow's call" , "Cartoon sound of a cow" , "Guernsey noise?" , "Cow's low" .)