Some get depressed. Some get aggressive. And some just “turn off” completely and have no reaction at all.

We don’t need science to tell us that horses have a variety of behaviors with which to express negative emotions. But a recent review of behavior studies by a French behavior researcher confirms that these negative emotions—and the way horses express them—can be a direct result of the way the animals are trained and managed.

“Although more research is needed, the elements we already have clearly indicate that we should consider equine welfare to be critical not only in the horse’s health and physiological state, but in his relationship with humans as well,” said Clémence Lesimple, PhD, researcher at the University of Rennes. Lesimple presented her findings at the 2014 French Equine Research Day held March 18 in Paris.

In her review of hundreds of horses in various behavior studies, Lesimple found that horses housed in individual box stalls with little or no access to other horses tended to be more aggressive toward humans, she said. This was also true of horses fed diets high in concentrated starch feeds and low in forage—probably because of the “frustration” of not being able to chew all day long as well as potential gastric pain, she said.

Furthermore, horses trained exclusively with negative reinforcement appear to make negative associations with humans, anticipating constraints they can’t control, said Lesimple. Certain training techniques and positions—as well as poor equitation style, especially of novice riders—can lead to chronic pain. Horses with chronic back pain showed more signs of depression, aggression, or learned helplessness (when they seem to “check out” of the environment that they have come to perceive as negative), she said.

“From their very earliest ages, horses develop an ‘appreciation’ of humans which is more or less positive, meaning that their perception of humans is associated with positive or negative emotions, but it is rarely neutral,” Lesimple said. While the research provides a strong link between poor welfare and negative interactions with humans, there is a positive side to the research, said Lesimple. Improving a horse’s welfare can not only improve a horse’s relationship with humans, but when started from the beginning it can help ensure a lifetime of positive perceptions of humans on the ground, in management settings, and under saddle.

“Anything we can do to improve a horse’s living conditions—providing hay if there is no grass, giving him access to open spaces and opportunities for social contact with other horses—are controllable parameters which could likely offer a simple solution to a certain number of behavior problems towards humans which currently occur far too often,” she said.

“Likewise, appropriate training and riding techniques associated with a positive context (positive reinforcement, for example), could actually make training a motivating, stimulating activity which is in itself a source of good welfare.”