Horses with wider loins and greater cannon bone circumference can bear weight better.
The amount of weight a horse can safely carry on its back depends upon a variety of physical traits. These may include the horse's size, conformation, body condition, age, the duration of the work to be done, as well as the speed at which the work is being performed.
There are a few methods that are currently being used to help estimate how much weight a horse can carry, however, little research evidence can be found to support these methods. The objective of the study conducted in Ohio was to determine whether horse height, cannon bone circumference, and loin width can be used as indicators of weight carrying ability in light horse.
Horses demonstrated higher work rates both at the trot and canter when carrying 25% and 30% of their body weight compared to carrying 15% or 20%. Heart rates after exercise differed when horses carried 25% and 30% of their bodyweight. Horses tended to have a greater change in muscle soreness and muscle tightness when carrying 25% of their bodyweight, with significant change demonstrated when carrying 30% of their body weight.
Loin width and bone circumference were negatively correlated with change in muscle soreness and tightness, suggesting that the horses having the wider loin area and greater cannon bone circumference became less muscle sore when asked to carry the higher weight loads.
This study shows that when horses are asked to carry over 20% of their bodyweight, the additional weight influences both work rate and heart rate, indicating higher work loads. Further studies using a larger data set will be necessary to assess the importance of loin width and cannon bone circumference when assessing weight carrying capacity in the riding horse.