They progress in leaps and bounds before eating cane up (8)
I believe the answer is:
antelope
'they progress in leaps and bounds' is the definition.
(antelopes bound along)
'before eating cane up' is the wordplay.
'before' becomes 'ante' (I've seen this in other clues).
'eating' means one lot of letters goes inside another.
'cane' becomes 'pole'.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'pole' backwards is 'elop'.
'ante' enclosing 'elop' is 'ANTELOPE'.
(Other definitions for antelope that I've seen before include "Odd toe panel of this hoofed animal" , "grazing animal" , "Springboks, say" , "Such as a gnu or eland" , "Hoofed mammal" .)