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How much weight can a horse comfortably carry?
It is a difficult question. Science provides some guidance, but there are several important caveats.
Anyone hoping for a simple formula will surely be disappointed, as there are too many variables in the equation, and many of them are subjective.
The most recent research to garner publicity was carried out in Cornwall, England.
Researchers from Duchy College produced findings, published in the latest issue of the Journal of Veterinary Behaviour, that suggested only one in 20 riders may be within what they described as the optimum weight range for their horse.
The study found that a third of recreational riders were potentially too big for their horse, leaving the animals at risk of back troubles and lameness. However, 63 per cent of riders in the survey fell within the satisfactory range for body weight, falling within 10-15 per cent of the weight of their mount.
The researchers from Duchy College, in Cornwall, assessed 50 horse-rider combinations from stables across Devon and Cornwall.
It has to be said that the researchers never set out in this particular study to come up with weight guidelines for riders. Their aim was to explore horse and rider body-weight relationships.
To that end, an industry practitioner proposed a 10 per cent rider-to-horse ratio for optimum performance, up to 15 per cent as satisfactory and a level of 20 per cent to be a potential welfare issue. Just 5 per cent of the riders involved in the study met the optimum threshold. Thirty-two per cent of the riders weighed more than 15 per cent of the weight of their animal, which is considered to pose a potential welfare risk.
The online reaction to the findings were swift, with some dismissing them out of hand. Many seemed not to grasp what optimum meant, believing that if they weighed more than 10 per cent of their horse’s body weight then they were unsuited to ride it.
The optimum riding weight is surely a rider weight at which the animal can perform to the best of its ability, such as jockeys in control of thoroughbreds.
Equitation scientists Dr Hayley Randle, who conducted the study with Emma Halliday, suggested guidelines be put into place to protect horses from overweight riders. She noted that guidelines for riding weights were not widely known by those in the horse industry.
“Since observed rider-to-horse body-weight ratios varied between 14.2 and 16.6 per cent, the suggested 10 per cent guideline appears unrealistic within the general riding population,” the authors noted.
There were currently no industry-wide guidelines for the suitability of rider weight to horse size, they added.
They said they hoped their findings would go some way toward allowing the development of a scientifically based guideline allowing informed decisions to be made on horse-rider suitability.
Some publicity in the mainstream media around the research played upon the sensitivity some riders have over their weight.
Suddenly, the issue was one of rider obesity, which was surely not the point at all.
Headlines emerged such as “The horses saddled with our obesity epidemic”, “British beasts of burden: Obese UK riders put horses’ health at risk”, and “Study: Horses injured by rider obesity”.
Some riders got it into their heads that, if they weighed more than 10 per cent of their horse’s body weight, they were potentially risking its welfare, when in fact the study declared that, on top of the 5 per cent that fell in the optimal weight range, 63 per cent were 10 to 15 per cent of the weight, which was rated as satisfactory.
It is understandable that some riders will be sensitive about their weight and, equally so, any suggestion they may be too heavy for their mount.
Researchers may one day deliver a rider-weight-to-horse ratio that meet welfare criteria, but it will surely only ever be a broad-bush measure. There are simply too many other factors at play.
What is the age of the horse? What kind of riding will be undertaken and for how long? Is the rider balanced and capable? What kind of conformation does the horse possess? Is the animal well-conditioned and adequately fed and watered? What breed is it? In what condition are its feet? What kind of saddle is being used and does its fit properly?
Science has not yet delivered a formula to calculate the rider-bearing capabilities of horses, but it has certainly provided some insights into the upper limits of load-bearing abilities.
American researchers found that horses forced to carry between 25 and 30 per cent of their body weight have more physical problems related to exercise than those who carry 20 per cent or less.
Horses carrying 30 per cent body weight showed a significant increase in muscle soreness and muscle tightness scores.
Such changes were less marked when they carried 25 per cent of their body weight.
Dr Debra Powell and her colleagues at the Ohio State University Agricultural Technical Institute, in Wooster, conducted a study in which eight horses, carrying up to 30 per cent of their body weight, were monitored during a standardized ridden exercise test in an indoor school arena.
The study used one mare and seven geldings, all of light-horse breeding and weighing between 391 and 625 kilograms. The horses ranged in age from 6 to 18 years.
After a five-minute warm-up, the horses were ridden at a trot (three metres per second) for 4.8km, followed by 1.6km at a canter (five metres per second).
The exercise schedule aimed to simulate a 45-minute workout typical of an intermediate-level riding school horse.
The animals’ heart rate, plasma lactate concentration and creatine kinase were monitored. Lactate is produced in the muscles during exercise. At low levels of work the body can metabolise it and so levels in the plasma remain low. However, as the work level increases the rate of lactate production exceeds the body’s ability to remove it and so concentrations rise. Creatine kinase (CK), an enzyme present in the muscles, is released into the blood as a result of some types of muscle damage.
An animal massage therapist assessed muscle soreness and muscle tightness before and after exercise.
The findings supported the view that horses can carry up to 20 per cent of their body weight without difficulty.
There was little difference between all the measures when horses carried either 15 per cent or 20 per cent of their body weight. However, the scientists started to detect differences when weight levels increased further.
The heart rate when horses carried 25 per cent or 30 per cent of their body weight remained elevated for longer after exercise. The serum CK level was also higher immediately after exercise, and also 24 and 48 hours later, in horses carrying 30 per cent body weight compared with those carrying 25% or less.
Powell and her fellow researchers, Karen Bennett-Wimbush, Amy Peeples and Maria Duthie, also investigated whether conformation affected weight-carrying ability.
The scientists looked at the horses’ height, the circumference of the cannon midway between the knee and fetlock, and the width of the back (loin) behind the saddle, between the last rib and pelvis.
They found that horses with wider loins and a thicker cannon bone circumference showed less muscle soreness and tightness when carrying the heavier loads.
The researchers stressed that it was a small study involving only a small number of horses, and suggested further investigations into the value of loin width, muscle depth and hoof size as an indication of weight-carrying ability would be worthwhile.
They concluded in the study, entitled Evaluation of Indicators of Weight-Carrying Ability of Light Riding Horses, that, for lighter riding horses, a total weight (rider, saddle, other equipment) not in excess of 20 per cent of the horse’s body weight was quite acceptable and did not appear to stress the horse.
Interestingly, that correlates with a military rule of thumb. In its 1920 Manual of Horse Management, the US Cavalry suggested a horse should not be asked to carry more than 20 per cent of its body weight. This assumed a combined weight of rider, saddle, bridle, and other equipment.
It goes without saying that cavalry units around the globe lived and breathed horses, but even that figure needs to be viewed in context.
First, cavalry horses were generally picked with quite specific requirements in terms height, body size, back length, hoof shape and bone to give them the best chance at standing up to the demands of service.
In Europe, there were major differences in the weight-bearing requirements of light cavalry and heavy cavalry.
At times, the attrition rate among horses in various conflicts around the globe from lameness soared, and horse shortages frequently saw the quality of the mounts decline.
The standard load on an American cavalry horse ran to 230-250 lbs, meaning most were required to carry more than 20 per cent of their body weight.
It goes without saying that the whole question is fraught, and an arbitrary percentage will only ever be the crudest of tool.
The research would seem to suggest that once a rider and their tack presses into the 15-20 per cent range of their horse’s body weight, they need to staying paying close attention to all the other factors that have a bearing on their animals’ ability, from fitness to conformation.
That unfortunately, leaves riders assessing their own performance in the saddle. How many riders would consider themselves unbalanced in the saddle? Almost certainly, practically none. Some may have an inflated view of their own riding abilities.
There is no simple answer, it would seem, except to err on the conservative side.