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.
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
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.
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.