Dr. Doolen grew up around horses in Montana and started taking care of birds and exotic animals at a young age. He worked as a professional photographer in Iowa until 1982, when his exotic bird rescue and breeding hobby inspired him to become a veterinarian to help advance exotic animal medicine, then in its infancy. He earned his DVM from Iowa State University College of Veterinary Medicine in 1991.

After graduation, Dr. Doolen remained at Iowa State University College of Veterinary Medicine for 3-1/2 years, working as an exotics clinician in the teaching hospital and developing an avian and exotics program. In 1994, he joined a general practice in New Jersey where he spent 15 years developing and directing an avian and exotics service. He joined NorthStar VETS in 2010.

An avid author and presenter, Dr. Doolen has written many articles and textbook entries, and lectures locally, nationally and internationally. He served as an adjunct assistant professor for five years at the University of Pennsylvania School of Veterinary Medicine, contributing to the development of the exotics program there.