Injury puts years on mother animal (6)
I believe the answer is:
damage
'injury' is the definition.
(I know that damage is a type of injury)
'years on mother animal' is the wordplay.
I cannot really see how this works, but
'years' could be 'age' (period of many years) and 'age' is located in the answer.
'mother' could be 'dam' (female parent of an animal) and 'dam' is located in the answer.
No letters remain.
This explanation may well be incorrect...
'puts' acts as a link.
Can you help me to learn more?
(Other definitions for damage that I've seen before include "Harm, impair" , "Deface, harm" , "Physical harm" , "Cost (slang)" , "To vandalise" .)