We know a lot less about the medical care of most zoo animals than we do about ourselves... or our domestic animals. Veterinary care of zoo animals has been largely trial and error. Part of it was using domestic animals as comparative models - domestic dogs for wolves and other wild canines, cattle for antelope, humans for other primates. A lot of it has been dumb luck and trial and error.
That, I'm sure, is how human medicine developed - trial, error, and dumb luck. What helped zoo medicine develop, however, was that dedicated professionals like Dr. Fowler were willing to compile the known data, research what wasn't known, and spread the knowledge, so that vets at zoos around the world could stop reinventing the wheel and starting building off of each others' knowledge and experiences. This has lead to increasingly better care for zoo animals (to the point where old age is the most common cause of death for many popular zoo species). The entire zoo community owes Dr. Fowler a tremendous amount of gratitude, and condolences to his family.