In the July 2009 edition of The Veterinary Journal ("Investigating horse-human interactions: the effect of a nervous human"), a team from the Department of Animal Environment and Health at the Swedish University of Agricultural Sciences in Uppsala presented a novel experiment in which they could test the effect of anxiety in humans on horses that were being ridden or lead. The horses taking part in the research were Swedish leisure horses of various ages, sexes and breeds, and the humans were of mixed sexes and ages, and had a variety of backgrounds with horses.
The experiment asked each human to lead or ride their horse between two points four times. Participants were told that just before their fourth pass an umbrella would open as they passed the assistant, but in fact the umbrella was not opened. Since the horse did not know about the umbrella, and since it did not open and so could have no effect on the horse, the researchers were able to determine if the effect caused by this expectation on the human could be felt by the horse.
In both cases where the horse was being led and ridden, the human’s heart rate increased and so did the horse’s, indicating that it somehow detected the human’s anxiety. In the wild, horses are in tune with the behavior of their herd-mates in order to swiftly react to threats. It would not be surprising if a horse could respond to the heart rate of a human that was riding it, since it may be able to physically sense this, but what is most interesting about this study is that even in cases when it was only being led by a human it also responded with an increased heart rate.