Gather the mother animal plays a protective role (5)
I believe the answer is:
Here is my best explanation:
'gather' is the definition.
('amass' can be a synonym of 'gather')
'a protective role' is the wordplay.
'protective role' becomes 'mass' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the mother animal plays' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for amass that I've seen before include "Accumulate, heap up", "Accrue, heap up", "Pile up", "Collect or gather", "Accumulate over time", "run up?", "Bring together", "Stockpile", "Stock up on" and "collect".)