An old hand at doctoring animals? (3)

I believe the answer is:

vet

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'an old hand' is the definition.
(I've seen this in another clue)

I can't explain the rest of the clue.

(Other definitions for vet that I've seen before include "Old soldier (inf.)" , "A small animal doctor" , "Check someone for suitability" , "A diminutive animal doctor" , "Dog doc?" .)

I've seen this clue in the Evening Standard.

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