Animal doctor near frisky warhorse (7)
I believe the answer is:
veteran
'warhorse' is the definition.
(I know that warhorse can be written as veteran)
'animal doctor near frisky' is the wordplay.
'animal doctor' becomes 'vet' (veterinarian).
'frisky' indicates an anagram.
'near' with letters rearranged gives 'eran'.
'vet'+'eran'='VETERAN'
(Other definitions for veteran that I've seen before include "American ex-soldier or old hand" , "Former member of the armed forces" , "One long experienced" , "Person with long experience, as in American army" , "he's seen a lot of service" .)