Vet ruled out mixed vegetables for dogs (7)
I believe the answer is:
beagles
'for dogs' is the definition.
(beagle is a kind of dog)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for beagles that I've seen before include "Short-legged hounds" , "Dogs" , "These hounds bag eels badly" , "Hunting hounds" .)