Mareike Becker-Birck and her research team tested cortisol levels, heart rates, and heart rate variability of 8 geldings from the French National Equestrian School in Saumur and their riders before and during dress rehearsals and performances. All events took place at the school in Saumur, so the location remained a constant.
Human heart rates increased much more during performance than during dress rehearsal, but horses heart rates increased the same amount during both activities, indicating that the horses did not pick up stress from their riders on event day.
Though cortisol levels were higher in the horses on performance day than on rehearsal day, they did not affect the horses' cardiac readings, according to the researchers. In fact, they surmised that the higher cortisol readings were do to more people coming around before the show to examine the horses.
"The presence of an audience caused more pronounced sympathoadrenal activity in riders than in the same tasks without spectators," Becker-Birck said. "So the spectators induced an acute stress response in the riders, but at the same time (caused) no additional stress on the horses."
Source: The Horse.com