Equestrian competitions at the 1968 Summer Olympics in Mexico City, Mexico featured team and individual competitions in show jumping, eventing, and dressage. Mexico City proved a challenging site since it was 2,300 meters above sea level, resulting in 30% less oxygen in the air. The horses at the 1955 Pan American Games, which was also held in Mexico City, arrived a few weeks before the Games to adjust, but had difficulty in the competition. However, racehorses that competed at the same location and who were shipped in the day before, and left the day after the race, performed fine. It was discovered that although horses would adjust immediately to the high altitude during the first few days after arrival, they showed weakness and decreased performance around Day 10, which continued to Day