Drop a little lower keeping length in mind (5)
I believe the answer is:
calve
'drop a little lower' is the definition.
(a calve is a lower, something which 'lows')
I don't understand the remainder of the clue.
(Other definitions for calve that I've seen before include "Give birth (to whales or icebergs)" , "Bear on farm" , "Give birth (eg to elephant)" , "Bring forth a baby cow!" , "bear on ranch" .)