Results from a survey, conducted by the authors as employees of the Burnet Park Zoo, show that very few captive elephants in zoos (18 in the USA) are trained for ride operations. Trained elephants are easily accessable for treatment, are less "bored", and overall are healthier than non-trained elephants, which may be manifested in a longer life span. The benefits derived from a well planned elephant training and ride operation clearly outweigh the costs incurred.
Moore, D. E., & Doyle, C. E. (1986). Elephant Training and Ride Operations, Part I: Animal Health, Cost/Benefit and Philosophy. Elephant, 2(2), 19-31. Doi: 10.22237/elephant/1521731987