The scientist who led a pilot study into the effect of rider weight on horses suggests future research is unlikely to deliver an ideal ratio.
“It depends on so many factors,” said Dr Sue Dyson, head of clinical orthopaedics at the Animal Health Trust’s Centre for Equine Studies in Newmarket, England.
These include the conformation, fitness and strength of the horse, the presence of any subclinical problems or overt clinical problems, the fit and suitability of the saddle, the ability of the rider, their balance and symmetry, their fitness and the type, duration and intensity of work and the footing and the terrain.
The study assessed gait and behavioural responses in six horses ridden by four riders of similar ability but different sizes. The riders were all weighed in their riding kit and were subsequently categorised as being light, moderate, heavy and very heavy.
The study indicated that problems were apparent in 30 minutes of flat work with the heavy rider, who was on average 16.7% of the horse’s body weight ratio. However, the saddles being used did not fit the rider.
“This does not mean that this is a reliable cut-off ratio,” Dyson stresses.
“We need to consider whether the combination of horse and rider are appropriate, regardless of weight and body mass index (BMI). Is the horse’s back of long enough length to accommodate a saddle long enough for the rider so that they can sit in the centre of the saddle?
“It is possible that with a longer saddle, enabling the rider’s bodyweight to be better distributed – assuming that the horse’s back is long enough to accommodate this – the ratio could be considerably higher.
“More work is needed to confirm the factors that influence the weight an individual horse can carry.”
Dyson says that while it is intuitive that a rider who is too heavy for a horse may harm its welfare, there are no scientific studies to support this under real-life conditions and no practical available guidelines for what is or is not too heavy.
“Previous studies have typically looked at the effect of deadweight, which is very different to a moving rider. The study also took into account that riders of differing size may ride a horse in the same saddle, which is not likely to fit all riders, therefore influencing their weight distribution.”
Weight, she says, is more influential than BMI.
“You can be obese without being unduly heavy. The effect on the horse is through weight and its distribution, which may also be influenced by height because of the way that height affects the rider’s position in the saddle.”
In essence, bigger riders need bigger horses.
Some of the horses in the study became temporarily lame when carrying the heavier riders.
“I had expected this,” Dyson says, “based on previous clinical observations over the years.”
“I have seen many horses ridden sequentially by people of very different weights and seen an immediate change in the way the horses moved.
“I have previous evidence of horses in full work with no underlying clinical problem showing transient lameness when ridden by a heavy rider. Horses with low-grade lameness when ridden by a lightweight rider may show much more obvious lameness when ridden by a heavier rider.
“The lameness was temporary, because it was a direct effect of the weight of the rider. It had resolved within 45 minutes and all horses moved at the end of the study as well or better than they did at the start when ridden by the light or moderate riders. However, if a rider of similar weight to the test rider rode the horse regularly then lameness may become a permanent feature.”
She said a very heavy rider was included in the study because there were many who rode horses. “We need to demonstrate what effect they may have. We had no idea whether, under the circumstances of this study, the threshold was going to be between moderate and heavy or heavy and very heavy.”
She said it would have been preferable in the study if all the saddles had fitted perfectly. “But we know based on a previous study that more than 50% of 506 horses in normal work had ill-fitting saddles; approximately 34% of horses I investigate on a weekly basis have ill-fitting saddles, so we need to know if a heavy rider accentuates any ill-effects of a poorly fitting saddle.
“It is also very unlikely that a single saddle on one horse could have fitted all 4 riders. This mimics what happens in the real world, e.g., a show pony being ridden in by an adult rider.”
A report on the pilot study can be read here.