Reams written about horses (5)

I believe the answer is:

mares

'horses' is the definition.
(female horses)

'reams written about' is the wordplay.
'written about' indicates an anagram (letters moved about before being rewritten).
'reams' with letters rearranged gives 'MARES'.

(Another definition for mares that I've seen is " Female horses".)

I've seen this clue in The Mirror.

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