Allan Leventhal came from a family of veterinarians, with one uncle and three cousins in the profession. That, combined with his love for animals, started him on his path to becoming a doctor in the field of animal medicine. After serving in the Army Air Corps during World War II, Allan took advantage of the GI Bill, enrolling at Cornell University. He made his way through both their pre-veterinary and veterinary programs to graduate first in his class and become Doctor Allan Leventhal in 1951. Upon graduating, Dr. Leventhal went to work as an intern at the veterinary practices owned by his uncle and cousins. On January 18, 1953, he borrowed one hundred dollars from his father-in-law and made a down payment on the property at 222 Boston Turnpike in Bolton. The first Bolton Veterinary Hospital was born on April 7, 1953 in a converted 600 square foot two-stall horse barn in the back yard of his house. The barn was heated by one small pot-bellied stove and served as the reception, examination, surgical, laboratory, treatment, and discharge areas of the new "hospital."

Dr. Leventhal was on call twenty-four hours a day, seven days a week.  He was able to manage with the help of his beautiful wife Dottie, who functioned as his surgical nurse, kennel attendant, telephone operator, and receptionist, all the while having an infant on her hip and a three-year-old wrapped around one leg.  Having the practice fifty feet from their home was ideal in many respects.  A serious surgical case could be monitored hourly all through the night and monitoring a whelping bitch was "a short hop to the hospital and than back to bed."  However, having the practice so close to home also meant clients banging on the door during the middle of the night and on holidays.  During the twelve years that he lived next door to his practice, Dr. Leventhal rarely felt able to relax enough to change into pajamas before going to bed.  He said "...if I chanced it, invariably I'd have to redress to tend an emergency."