Encouragement given by nice vet in novel (9)
I believe the answer is:
incentive
'encouragement' is the definition.
(something incentivising certain behaviour)
'nice vet in novel' is the wordplay.
'novel' is an anagram indicator (letters in a new or novel order).
'nice'+'vet'+'in'='nicevetin'
'nicevetin' anagrammed gives 'INCENTIVE'.
'given by' is the link.
(Other definitions for incentive that I've seen before include "encouragement" , "Payment to improve" , "Stimulus" , "Motivating payment" , "Motivational reward" .)