Seven Taishuh ponies (5 mares and 2 geldings) and their rider were fitted with a marker and recorded by 2 high-resolution digital DVD cameras as they were trotting along a straight course. Each horse performed 7 tests: 2 tests with 154 pound loads and 5 tests with random weights between 176 and 265 pounds. Among ponies, symmetry in the 265 pound test was significantly lower than that in the 154 pound test, and stabilities during the 220 and 265 pound tests were significantly less than that in the 154 pound test. The time lag between the time series of horse and rider in the 265 pound test was significantly greater than that in the 154 pound test.
These results suggests that the maximum permissible load weight of the Taishuh pony at a trot over a short distance is less than 200 pounds, which is 43% of the bodyweight of the pony.
Although other research has shown that horse can safely carry up to 30% of their body weight, it s generally accepted that a horse can carry up to 20% of their body weight. However, there are other factors than just weight that impact how much weight a horse or pony can carry, including conformation of the horse, the horse's fitness level, rider fitness, and rider ability level. For example, a fit horse with ideal conformation can carry more weight if the rider is also fit and well balanced.
Summarized by: Krishona Martinson, PhD, University of Minnesota