Tevis Research Changes Thinking on how much Weight a Horse can Safely Carry

Conventional wisdom states that a horse should carry no more than 20% of its weight, including tack. That’s the number when you ask Google, although there’s very little science behind it. For a horse weighing 1,000 pounds that would mean no more than 200 pounds. The Horse-Rider Weight Calculator on http://www.Goodhorse.com uses a similar algorythm.

Another study, of just six horses, states that gait asymmetry develops as weight increases. These researchers concluded horses could carry up to 29% of their body weight before showing issues. Of course, carrying “dead weight” may be a factor in the results.

Matsuura colleagues from Kitasato University and the Towada Riding Club, studied Japanese horses at the walk and trot. The six study mares—relatively small Hokkaido native horses—averaged 14.1 hands in height and 340 kilograms (750 pounds) in weight. They were ridden by the same 66-kilogram (145-pound) rider in all tests, but researchers loaded the horses progressively with more and more weights, with a maximum of 130 kilograms (287 pounds) total weight. Researchers evaluated the horses with an accelerometer as they moved in a straight line at predetermined, fixed speeds.

Their results showed that the horses appeared to manage loading relatively well up to 95 kilograms (209 pounds). At 100 kilograms (220 pounds), the horses showed a significant lack of symmetry as represented by uneven peaks in the acceleration readings. In order to leave a safety margin for tack, equipment, and clothing, Matsuura said he and his colleagues recommend keeping weight load under 100 kilograms for these horses.

Still another “pilot study” (read small study, again only with six horses) concluded that,

The influence of rider to horse bodyweight ratios on equine gait and behaviour: a pilot study1 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.  Their body mass index (BMI) was also calculated. The BMI calculation divides an adult’s weight by their height squared and the score is used to assess healthy weight.

Rider Weight Study
In this study, all riders, regardless of weight or height, used the same saddle. That alone could cause pressure points on a horse’s back, since the balance point is not the same for all riders.

Each rider rode each horse in its usual tack and performed a set pattern of exercises comprising mainly trot and canter. Gait, horse behaviour, forces under the saddle, the response to palpation of the back, alterations in back dimensions in response to exercise, heart and respiratory rates, salivary cortisol levels and blink rate were assessed for each combination.

The riding tests for the heavy and very heavy riders were all abandoned, predominantly because of temporary horse lameness. This was likely to have been induced by bodyweight rather than BMI, given that the heavy and moderate riders had similar BMIs, both being classified as overweight, yet only one of the moderate rider’s tests had to be abandoned. An ethogram, developed by Dr Dyson specifically to assess behavioural markers which may reflect pain in ridden horses3, was applied. The scores which may reflect pain were significantly higher in the horses when ridden by the heavy and very heavy riders.  Rider Weight Debate: What Can Latest Research Tell Us

Of course, as you can see from the photos, they used the same saddle for all the riders. Properly fitting tack for both horse and rider can make a huge difference. Some of those riders are really jammed into those saddles. However, I find it hard to believe that they observed measurable lameness at the walk and trot after just 30 minutes of riding.

Tevis Data Paints a Different Picture

Cougar Rock Tevis Cup
Somehow I think that data collected from 360 horses over a 100 mile course is more meaningful than six horses ridden for 30 minutes.

The Tevis Cup, a 24 hour, 100-mile ride over the rugged trail from Lake Tahoe to Auburn is a singular challenge for both horse and rider. It also is an interesting test of how rider weight impacts a horse’s soundness.

The peer-reviewed 1995-96 Tevis Weight and Body Condition Score study, published in the equine exercise physiology journal, ICEEP, collected close to 1000 data points on at 360 horses (10 stallions, 84 mares, 266 geldings), primarily of Arabian breeding, ranging from 5-22 years old. A  rider weight ratio was calculated as the rider weight divided by horse body weight. Some of these findings fly in the face of the pilot studies.

  • Rider weight and rider weight ratio had no effect on overall completion rates among all horses (p>0.05).
  • Among horses successfully completing the course, rider weight and rider weight ratio had no effect on finish time or placing (p>.05).
  • Among horses who were eliminated, rider weight and rider weight ratio had no effect on miles completed before failure (p>.05).
  • Body weight of the horse had an effect on completion rate, in that horses with heavier body mass had a higher incidence of failure due to lameness (p<.001).
  • Condition scores had a significant effect on completion rate (p<.001).
  • Miles successfully completed increased 19.88 miles for each incremental increase of 1 in condition score (p<.001).
  • Within the group of unsuccessful horses, there was a significant difference in condition score between horses who failed due to metabolic and non-metabolic factors (p<.001).
  • It was concluded that condition score is a more important factor in endurance performance than has been previously believed, and that condition score is a more important factor than is the weight of the rider, or the rider weight in relation to the weight of the mount.

The data used in this study were rigorously collected:

All participants were given thorough physical examinations by a veterinary committee during the check-in period. Heart and respiratory rates, capillary refill time, hydration, mucous membrane color, and results of auscultation and musculoskeletal examination and other observations were recorded on a rider card carried on the horse through the event. Horses were walked and trotted on firm dirt footing and gait irregularities noted. Horses which did not meet criteria were disqualified from competition prior to the start. During the event, horses undergo veterinary examination at eleven additional checkpoints and are eliminated if they are judged as lame, experiencing metabolic failure, exceed maximum time limits, or otherwise do not meet veterinary criteria. Riders experiencing injury, illness or other difficulties may also voluntarily withdraw from competition.

A follow up study was conducted by Dr. Garlinghouse in 1998, The Influence of Body Measurements and Condition Score on Performance Results During the 1998 Tevis.  The second study was conducted on 193 horses, mules and ponies, aged 5-22. Results confirmed the findings of the earlier study.

Approximately 11 to 18 hours prior to the start of the event, a veterinary committee examined each entrant for normal gait and metabolic indicators, the results of which were recorded on a card and utilized at each of the eleven additional checkpoints. Horses which failed to meet veterinary criteria at any of the respective checks were disqualified based on four categories; Lame, Metabolic (experiencing stress related to exhausted horse syndrome, such as dehydration, tying-up, poor gut motility or synchronous diaphragmatic flutter), Rider Option or Overtime (failing to reach checkpoints within a given time allowance).

Performance data were compiled by race management throughout the event, and included time to reach each checkpoint, overall placing, and results of veterinary examination. Reasons for disqualification were recorded for those horses not meeting veterinary criteria, or otherwise unable to continue.

Weight Carried Tevis
In this chart, Group S represents those who completed the course within the 24 hours allotted.

The results of this study would suggest that horses in good condition are capable of carrying relatively heavy loads, whether as rider weight or in their own body weight, over a 160-km course without the deleterious physiological effects seen in maximal exercise.

Body weight of the horse had an effect in that as body weight increased, failure due to lameness increased. Mean cannon bone circumference measurements of 19.25±.71 cm were similar to values of 18.83±.66 cm reported in Garlinghouse and Burrill. Circumference did not increase proportionately as body mass increased. These results suggest that increased body weight without a proportionate increase in the cross sectional area of the metacarpus increase the incidence of exercise-induced trauma and biomechanical failure.

Based on the Tevis studies, I think that researchers need to rethink their methodolgy and their conclusions. In the meantime, make sure your saddle fits, develop enough core strenth and balance to be responsible for your own weight, then go ride your horse and don’t overthink your rider-to-horse weight ratio.

11 thoughts on “Tevis Research Changes Thinking on how much Weight a Horse can Safely Carry

  1. I agree that (n=6) in the first study (Japanese) isn’t a large enough sample to really make sense of the data, but it does show, if nothing else, that ‘more data is needed”. And it is an interesting tack to take.
    Having done statistics as part of being a field biologist, as well as having done field data collection in the Army, I can say that “there is no such thing as sufficient data.” But the Tevis samples ARE substantial in at least the sample size. I think there’s a statistical artifact in the Tevis study in that the vast majority of horses sampled are Arabians or crosses. The study itself is excellent but I would like to see something that includes horses from other breeds…i.e TB’s, QH’s etc. Whether that will be done, I don’t know, but I will say that the both studies gave me a lot to think about. Conditon and cannon bones…those two things jump out at me. Thank you for this very interesting post.

  2. I agree that the preponderance of Arabians and Arab crosses does skew the data, but it’s an impressive amount of horses studied and the analysis of condition/lameness was far more rigorous than the other studies. Dr. Garlinghouse is well respected in the endurance community and I have a lot of confidence in her conclusions. She also mentioned how expensive it is to do these studies, which is why so few of them are done.

    1. It’s a selection, though, based on the horses most suitable to the task. That’s not quite a ‘skew’, just that Arabians are the best endurance horses widely available – maybe Akhal-Tekes are as good, but they are rare.

  3. She’s right…studies such as hers are expensive, mostly because horses aren’t high priority for most of the country. I’ve been studying western meadowlarks for several years. Had to buy all my equipment, get a banding license, pay for the permits that everyone insists are needed…the Feds, the State, the USGS Dept of Interior, Fish and wildlife, county…..oh for heaven’s sakes.
    I’ve read some of Garlinghouses papers in the past. You’re right, she’s a good scientist. I didn’t mean to sound disparaging or dismissive of her study, she did good work.

  4. I am flabbergasted that the researchers have only now concluded that conditioning the horse was such an important factor… It seems obvious a fit horse of the same size and weight would be able to manage working under saddle better than an unfit horse….

    1. But in the Tevis studies nearly all of the horses that completed the trial were carrying 20% or less of their weight. The highest ratios were in the lame group. Yes, yes statistical analysis… but there is more to the story than the summary explains.

  5. My takeaways from this: horse conditioning (endurance fit) allows for strength to carry heavier loads. I think the 20% guideline we are used to seeing is more for the casual rider on a weekend warrior type of horse, not one that is properly fitted up for the workload it’s expected to perform under at peak season (competitions, shows, etc).

    1. For sure, horses need to be fit to do the job, but I also think there is a lot more leeway in the “guidelines” so if you’re talking about an experienced, balanced rider, and a horse that isn’t a pasture puff, it’s not such a huge deal. Look at all the smaller breeds (Arabians, QH, some of the gaited breeds) who carry large men. Of course, I’m not advocating that horses should be overloaded or ridden into the ground.

  6. I’m not sure this study can be applied to today’s average rider. Horses and riders who qualify for Tevis and actually then compete are both in exceptionally great condition. Tevis is known as being one of the toughest endurance competitions in the world. There are no unfit horses or unfit riders. I’m not sure there are ever even any overweight horses or riders. Certainly this is a significant factor influencing the results of the study.

  7. All this is interesting, I have placed in several LD’s, I ride a paso 14’3 hands, I always get grief because I am 6’3″ and am 260 lbs. She and now he (now 24 years old) have done great on all these rides. What is suggested for me as a rider being this big. Help. Im really like to place and am very fit. I like paso fino’s for their get going, speed, endurance, agility. Kurt 62 years young. Geez really.

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