Horses carrying their regular riders appeared to cope well when the rider’s weight was increased by up to 25 percent, researchers report.
The findings add an interesting twist to the ongoing and often sensitive debate around how much weight a horse can comfortably carry.
However, the European research team that carried out the study, involving 20 horses and their riders, stressed that the results needed to be kept in perspective.
The maximum rider-to-horse weight ratios in the study were 15 to 23%, even with the additional weight carried by the riders, and the exercise intensity was relatively low – a standard dressage test.
“Thus the results should not be extrapolated to other weight ratios and exercise intensities,” Janne Winther Christensen and her colleagues reported in the open-access journal, Animals.
The influence of rider weight on horse welfare, health and performance is often debated, they noted.
The authors said recent studies had reported significant changes in physiological and gait parameters in horses when exposed to increased rider weight during moderate to high-intensity exercise
For their study, they measured the effects of increasing the weight of the regular rider by 15% and 25% on horse behavior, gait symmetry and physiological responses during a dressage test lasting just over five minutes.
They measured levels of the stress hormone cortisol in each horse’s saliva, as well as their heart rate, heart-rate variability, behavior and gait symmetry.
The research involved 20 female riders and their horses – six mares, 12 geldings and two stallions.
All horses were active riding and competition horses.
Rider weight in all cases included tack for the calculation of rider-to-horse bodyweight ratios.
The initial average rider-to-horse body-weight ratio was 15.3%, ranging from 12% to 19%. The added 15% produced an average rider-to-horse bodyweight of 17.2%, with a range of 14 to 21%.
The added 25% took the average to 18.5%, with a range of 15 to 23%.
The added kilograms in all cases were carried in a weight vest.
On the first day, all horses were assessed by a vet to ensure soundness, and saliva samples were taken to get baseline cortisol levels.
Heart-rate monitoring equipment was then fitted and the horses performed a baseline lunge test with the same amount of physical exercise as the riding test to be performed on the following three days, under the different weight scenarios.
All riding tests were recorded on video for later behavioral analysis.
“Cortisol levels increased in response to exercise, but we found no effect of the weight treatment,” the researchers reported.” That is, cortisol levels did not increase when the rider became heavier.
“Behavior, heart rate and gait symmetry also did not differ between treatments.”
There was, they said, large individual variation in conflict behavior, but no effect of weight treatment.
“We conclude that increasing the weight of the regular rider by 15% and 25% did not result in significant short-term alterations in cortisol, heart rate, behavior and gait symmetry in horses during low-intensity exercise.”
The study team says further studies are required to develop appropriate guidelines for rider weight.
“We conclude that increasing the weight of the regular rider by 15% and 25% did not result in significant short-term alterations in the measured parameters.”
Discussing their findings, the authors said it was interesting that the rider-to-horse bodyweight ratios in their study overlapped with the ratios in a study conducted by British researcher Sue Dyson and others, where the heavy rider was 15.3 to 17.9% of the horse’s bodyweight.
“In that study, all riding tests with the heavy rider were abandoned on welfare grounds, based on a subjective scoring of lameness and behavioral markers of pain. The result was not replicated in our study, although the rider-to-horse bodyweight ratio was 15-23% in the +25% treatment.
“The duration of exercise (including warm-up, riding test and gait symmetry testing) appear to be similar in the two studies.
“However, we could not detect changes in gait symmetry in (our) study.”
This, they said, may relate to differences in the seat position of the riders, as the riders in the present study were sitting compared to the use of the rising trot in the study by Dyson and her fellow researchers.
“Rising trot is known to induce movement asymmetries in the horse that may not be related to pain.
“Our study was a crossover study where each rider rode her own horse in each treatment, whereas four riders of different weight comprised the treatment in Dyson et al.”
Rider skill and balance as well as other factors, such as individual saddle fit, are likely to influence conflict behavior and weight-bearing capacity in horses. Isolating the effect of rider weight while keeping other factors identical is necessary to gain knowledge of the effect of increased rider weight.
“In our study, the large individual variation in cortisol concentrations and especially in conflict behavior likely reflects individual rider style.
“A larger study with a number of riders of the same weight, riding the same horses in a standardized test would enable an analysis of the effect of rider style.”
The researchers said the surprisingly similar heart rates of the horses in the different treatments in their study suggest that the increased rider weight did not impose a significantly higher physical workload on the horses.
“Given the low exercise intensity in the present study, one should not extrapolate the results to other exercise intensities and disciplines.
“Additionally, there may be long-term effects of an increased weight load, and further studies are required to study long-term effects on horse health and performance.”
The study team comprised Christensen, with Aarhus University in Denmark; Suzie Bathellier, with Agrocampus Ouest in Rennes, France; Marie Rhodin, with the Swedish University of Agricultural Sciences; Rupert Palme, with the University of Veterinary Medicine, Vienna; and Mette Uldahl, with Vejle Hestepraksis in Fasanvej, Denmark.
Christensen, J.W.; Bathellier, S.; Rhodin, M.; Palme, R.; Uldahl, M. Increased Rider Weight Did Not Induce Changes in Behavior and Physiological Parameters in Horses. Animals 2020, 10, 95.