Grass originally maintaining all rare male sheep (6)
I believe the answer is:
marram
'grass' is the definition.
(marram is a type of grass)
'originally maintaining all rare male sheep' is the wordplay.
'originally' suggests taking the first letters.
'male sheep' becomes 'ram' (a ram is a male sheep).
The initial letters of 'maintaining all rare' is 'mar'.
'mar'+'ram'='MARRAM'
(Other definitions for marram that I've seen before include "Coarse grass on sandy beaches" , "Sea grass" , "Grass of the seaside" .)