“Dog kennel” means any lot, building, structure, enclosure or premises whereon or wherein four or more dogs, four months of age or older, are kept or maintained for any purpose whatsoever, provided, however, that if other animals or birds or fowl are bought, sold or bartered, the classification to apply shall be that of a pet shop; and provided further, that this definition of dog kennel shall not be construed as applying to a duly licensed veterinary hospital nor to the San Luis Obispo County Humane Society. (Prior code § 4003.1)