Animals not climbing broken stair (7)

I believe the answer is:

nutrias

'animals' is the definition.
(nutria is a kind of animal)

'not climbing broken stair' is the wordplay.
'not' becomes 'un' (prefix meaning 'not').
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'broken' indicates an anagram.
'un' back-to-front is 'nu'.
'stair' anagrammed gives 'trias'.
'nu'+'trias'='NUTRIAS'

I've seen this clue in The Daily Express.

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