While adding up to 25% more rider weight didn’t negatively affect the horses in this study, researchers cautioned that it could in the long run.
“This is contrary to what we expected,” she explained during her presentation at the 15th annual International Society for Equitation Science (ISES) conference, held Aug. 19-21 in Guelph, Ontario, Canada. “However, it remains to be seen what happens with increased weight over the long term, as well as at higher exercise intensities.”
In their study, Christensen and her fellow researchers observed 20 horses longed and ridden by their usual riders in a basic dressage test in three gaits. They equipped the riders with metal weight bars fitted into a vest strapped onto the riders’ torso to increase their personal body weight by 15% and 25%. The scientists recorded the horses’ behavioral and physiological parameters during longeing and ridden dressage tests, with and without the added weights.
They found differences in behavioral signs of stress (head-tossing, tail-swishing, mouth-opening, etc.) from horse to horse but not within the same horse-rider pair across the different rider weights, Christensen said. Salivary cortisol levels also didn’t suggest significant changes in stress levels despite a minor rise. And heart rates were very similar, regardless of the amount of weight carried.
“I had expected the heart rate to increase with the added weight because the horses would have to work harder,” she explained. “I was wrong. There was absolutely no difference when we added the extra weight to the horses.”
It’s worth noting, however, that these rider-weight increases resulted in less than 10% difference in the total horse-rider weight ratio, said Christensen. Without added weight, the horses were carrying an average of about 15% (ranging individually 12-19%) of their body weight (for this study population of all women riders and primarily Danish Warmblood horses). With the maximum extra weight added, the average amount across all horses only reached 18% of the horses’ body weight (ranging individually 15-23%). Other studies have noted that horses tend to develop gait asymmetry with increasing weight ratios, with one study finding significant changes when the ratio surpassed 29%.
While the results suggest that adding up to 25% rider weight doesn’t seem to have a negative effect on horses that might not be true over the long-term, said Christensen. “We only measured the acute effects and at a relatively low exercise intensity,” she said.
Individual differences—such as the starting weight ratio in the horse-rider pair or the horse’s health status—could also create issues that the scientists didn’t see in this study, Christensen said.