A joint complaint's covered one lot of rodents (7)

I believe the answer is:

agoutis

I'm a little stuck... Click here to teach me more about this clue!

'lot of rodents' is the definition.
'agoutis' can be an answer for 'rodents' (I've seen this before). I'm unsure of the 'lot of' bit.

'a joint complaint's covered one' is the wordplay.
'joint complaint's' becomes 'gouts' (gout is a kind of health problem. I am not sure about the 'joint' bit.).
'covered' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'gouts' enclosing 'i' is 'goutis'.
'a'+'goutis'='AGOUTIS'

Can you help me to learn more?

(Other definitions for agoutis that I've seen before include "More than one animal" , "Rodents" .)

I've seen this clue in the Sydney Morning Herald.

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