Old soldier very good to animals? (3)

I believe the answer is:

vet

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

'old soldier' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for vet that I've seen before include "Ex-serviceman" , "animal doctor to > investigate" , "Screen" , "Check someone for suitability" , "Dog doc?" .)

I've seen this clue in the Evening Standard.

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