When it comes to considering how much weight a horse can carry, the number on the scales is just one factor to consider.There are many things to bear in mind when calculating whether a rider is a suitable size for a horse or pony and matching a jockey to an appropriate mount. These include features of both the rider and the horse, as well as the intended workload and use of the horse, plus the riding conditions, tack fit and more.Assessing how much weight a horse can carry and what a suitable horse riding weight limit is for them is a complicatedtask, but one that should beaddressed when youtake care of a horse if equine welfare is to be prioritised.Size rather than weightUnderstandingwhether a rideris an appropriate weight fortheir horse is a tricky and emotive topic, but one that is becomingly discussed more openly.It is not about whether a rider is fat ornot, its about whether theyre riding ahorse that is fit for the purpose required ofit, says Dr Anne Bondi, founder and director of The Saddle Research Trust.The terms weight andheavy are very emotive, and itsimportant to focus on the recognisedfacts, not emotions.Tall riders are just as likely to have a negative impact, so I think we should talk about rider size, rather than rider weight.How much weight can a horse carry?Dr Bondi devised a traffic lightsystem to help assess whether a horse iscarrying an appropriate load. The systemuses the riders weight ratio, which can becalculated by dividing the riders weight(ideally including tack) by the horses, andexpressing that figure as a percentage.GreenFor optimum performance (working close to or at its physiological limits without significantly increasing his risk of injury) and to be graded green, the horse should be carrying around 10% of their weight.AmberHowever, 15% is a much more common scenario, and this is graded amber.RedHorses carrying 20% of their weight are graded red as their welfare may be compromised.These guidelines are based on knowledge of the research that has taken place in this field to date, but these are my own views, explains Dr Bondi. We do not yet have scientific evidence for definitive figures due to the huge number of variables involved.There is concern about the message such ratios might give because it needs scientific basis, but it may be too complex to ever be able to provide accurate, suitable limits.In the meantime, the industry needs some guidance and I believe that this is a good place to start.Factors affecting horse riding weight limitDr Bondi stresses that each combination of horse and riderwill have different criteria dependingon their circumstances and that weightratios must be considered alongsideother important factors, including:Horse ageIf their musculoskeletal system isimmature, or the horse is a veteran, theywill be at greater risk of strain injury.The horses weight should be optimum.Type of horseThe horse must have a strongenough physique if they are to carry extraweight. Cannon bone circumference canbe used as a guideline, with the idealratio suggested as being 20cm per455kgs of bodyweight.BreedSpecific traits in certain breedscan offer an advantage in somecircumstances. The Arab, for example,has efficient metabolic features andgood running economy that may meanit can carry higher loads over longerdistances more easily.ConformationA dipped back, forexample, is a weakness that can put thehorse at higher risk of strain, whereas awider loin is believed to be desirable forendurance. The horses posture alsoaffects efficiency.Horse soundnessSome pathologicalconditions indicate a horse should becarrying easier (lighter) loads, which affects their horse riding weight limit.Rider sizeIts not just a case of how much weight a horse can carry; the riders weight, heightand the relative length of their limbs totheir upper body all influence thehorses performance throughdistribution of forces.Rider skillIn a balanced posture in thecentre of the saddle, the riders weightwill be close to the horses centre ofmass, and theyll be more able to carry it.The unbalanced load, by being out ofsynchrony with the horses movement,is likely to increase peak forces.Saddle fitAn incorrectly fitted saddle will adverselyaffect weight distribution on the horses back. The designshould contribute to the avoidance ofpeak pressures by providing a large,smooth and soft bearing surface. The weight of the saddle should be included when considering a horse riding weight limit.Horse fitnessFitness and preparation is an important factor. Working ona variety of surfaces and terrain isneeded to avoid repetitive strain injury.Workload (intensity and type)High impact activity increasesforces exerted on the horse by up totwice its own weight, while longerdistances and times make the horsemore vulnerable to injuries.TerrainThe effects of hill work on a horse aresignificantly higher than exercise onthe flat, and energy costs increase assurfaces become more uneven.Environmental factors such as heatshould also be considered.Rider skill and horse riding weight limitIf a rider is too tall for their horse, they could unbalance the horse much more easily and place excessive stress on the horse in the same way [as a too-heavy rider], says equine vet and former BEVA president Lucy Grieve.Although a more skilled rider will be able to maintain balance more easily than an inexperienced one, and so reduce the risk of damage to the horse, the potential is still there and should not be ignored.Riders at any level should endeavour to be the appropriate weight for their horse and/or choose a horse which is appropriate for them, and be as fit and balanced as possible if they wish to avoid putting the horse under undue physical stress and therefore pain.Rider weight: the researchSome studies have inferred that increased rider weight is less influential than other factors.A 1999 study Relationship of body condition score to completion rate during 160 km endurance races sought to find if rider weight influenced completion rate during 160km endurance races.It found that of 360 horses, rider weight and rider weight ratio had no effect on overall completion rates among all horses.It was also found that among the horses successfully completing the course, rider weight and rider weight ratio had no effect on finish time or placing.Another paper, entitled Increased Rider Weight Did Not Induce Changes in Behavior and Physiological Parameters in Horses and published in 2020, evaluated the effect of increased rider weight (+15% and +25% of the regular riders bodyweight) on horse behavioural, physiological and gait symmetry parameters during a standard dressage test.Data from 20 combinations was analysed and the researchers found that increasing the weight of the regular rider by 15% and 25% did not result in significant short-term alterations in the measured parameters.They stressed that maximum rider:horse weight ratios were 15-23% and the exercise intensity was relatively low; thus the results should not be applied to other weight ratios and exercise intensities.Workload and horse riding weight limitHigh impact work can increase the risk of injury, particularly if coupled with a larger rider. Joint care is essential. Overloading a horse risks damage to support structures of the limb, and hyper-extension of the fetlock, due to the weight of horse and rider, plus the reaction forces of the speed or height of the jump.Horses carrying extra weight are more likely to sustain injury, tire more quickly and make mistakes, explains Dr Bondi.This is not often taken into consideration, but mistakes can be fatal for example in cross-country.While risks are increased by more demanding work, horses in light exercise should also carry an appropriate load.Gentle hacking will have a lower impact on the horse, but if repeated long term with larger loading it can have a cumulative effect.Signs that a horse is carrying too much weightDr Bondi refers to a list of behaviours that are likely to reflect musculoskeletal pain if eight or more are displayed.A study looked at the effects of different rider sizes and found that all the horses demonstrated increased behavioural markers with larger riders, she says.The behaviours include:Repeated changes of head positionHead tiltingGoing in front or behind of the vertical for 10 seconds or longerHolding the ears back for five seconds or moreClosing or half closing the eyes for more than a few secondsFrequent blinkingExposure of the white of the eyeExhibiting an intense stareOpening their mouths for 10 seconds or moreHolding the bit to one sideClamping the tailSwishing the tailA rushed or slowed gaitHindlimbs not following the track of forelimbsRepeated changes of leg in canterSpontaneous changes of gaitRepeated stumbling or toe draggingSudden changes of directionA reluctance to move forwardRearingBuckingAs a vet its become increasingly common for me to see overweight horses and, sadly, we know that the human population has been demonstrating the same trend, adds vet Lucy Grieve.When we look at the effect rider size has on the horse, it can become a specific concern that we ought to be addressing.Awareness is growingAwareness about how much weight a horse or pony can carry is growing. In showing, for instance, several organising committees have cracked down on larger adults competing on small ponies.In 2022, Equestrian Australia revealed its Guide to Horse Capacity to help gauge whether a rider is an appropriate size and weight for their mount.Last year, The Suitably Mounted Group (SMG) launched a survey exploring the factors that should be considered when matching riders with horses or ponies.The SMGs Research Working Group, comprising Dr David Marlin, Dr Jane Williams and Lorna Cameron, devised the survey to capture the views of equestrians about which factors are the most important to consider when aiming to match riders with horses.The results of the survey will be shared by Your Horse as soon as they are available.There is a horse suitable for most ridersHowever, there is still a lot to be done. Tony Tyler, deputy chief executive of World Horse Welfare, said riders must recognise that every horse has a finite maximum horse riding weight limit it can carry and beyond that discomfort and harm can occur.There is a horse suitable for most riders, and percentage guides are a good starting point, but we must also be aware that each horse needs to be treated as an individual, he says.More research is needed on effects of rider size on the horse in the short- and long-term and, in the meantime, we must listen to our horses and be prepared to acknowledge and make changes if our size is negatively impacting on them in any way.Find out more about The Saddle Research TrustRelated contentHow a horses joints work plus vet advice to keep them healthyIs it bad behaviour or could your horse be asking for help?How to check the fit of your saddle *VIDEO*What you need to know about bridle fit and horse head anatomy *VIDEO*Main image ShutterstockThe post How much weight can a horse carry? appeared first on Your Horse.