"There have been many cases in the past where I know I waited too long. I can assure you that's not the case here," he told the press conference in which details were given of Barbaro's passing.
Alex Brown, who attended the conference, said it was clear that the three people who addressed the conference - Richardson and Barbaro's owners Roy and Gretchen Jackson - were devastated by the turn of events.
"There were times during some of Dr Richardson's responses that you could tell it was tough for him to maintain his composure," Brown said.
The conference heard how Barbaro was euthanised in his support sling after his regular morning feed of grass.
Richardson explained the recent complications and the further surgery that was required.
Barbaro was clearly distressed by his condition overnight, Richardson explained.
"We did what we said ... if we couldn't control his comfort we wouldn't go on, and that's why the decision was made."