Piece from the i : "Fertility's a little lower" (6)
I believe the answer is:
heifer
'a little lower' is the definition.
(I've seen this before)
'piece from the i fertility's' is the wordplay.
'piece' says the answer is hidden in the clue.
'HEIFER' is hidden within 'from the i fertility'.
(Other definitions for heifer that I've seen before include "Farm animal" , "part of stock" , "a little lower" , "Female bovine that has not given birth" , "Young cow which has not yet given birth" .)