1 in 55 obstructing animal rescue (7)
I believe the answer is:
deliver
'rescue' is the definition.
(synonyms)
'1 in 55 obstructing animal' is the wordplay.
'd' becomes 'I' (Roman numeral).
'in' means one lot of letters goes inside another.
'55' becomes 'LV' (Roman numerals).
'obstructing' is an insertion indicator (inserted letters interrupt or obstruct the word).
'animal' becomes 'deer' (deer is a type of animal).
'i' put inside 'lv' is 'liv'.
'liv' going within 'deer' is 'DELIVER'.
(Other definitions for deliver that I've seen before include "Bring into the world - set free" , "Bring (letters, etc)" , "Formally hand over" , "Handover" , "Free; supply" .)