I frequently see questions on on-line forums where people ask if they are too large or too heavy for their horse.

National Reining Horse Association Hall of Famer Bob Loomis doesn't seem to be causing his horse any problems.

I’ve also seen some flat out misstatements such as, “Thoroughbreds can only carry 145 pounds.” If that were true, mine would have collapsed a long time ago right along with a number of small Western reining horses who carry some pretty large riders.

Finally, there is some research on the subject. Okay, the study was small, including only 8 horses, but the data provides some interesting insights. The study, Evaluation of Indicators of Weight-Carrying Ability of Light Riding Horses, was published in the Journal of Equine Veterinary Science , Volume 28 , Issue 1 , Pages 28 – 33 and authored by Dr Debra Powell and colleagues at the Ohio State University Agricultural Technical Institute, Wooster, OH. I do not have access to the entire article, but have read the abstract and articles that summarize the findings.

In short: Horses that carry 25-30% of their bodyweight (including rider and tack) have more physical problems related to exercise than those horses carrying 20% or less. In particular, horses carrying 30% body weight showed a significant increase in muscle soreness and muscle tightness scores.

The test was conducted using 8 horses that each performed a standardized exercise test in an indoor arena. The regime was judged to by typical of a 45 minute work period for an intermediate level riding school horse.

According to an article in www.horsetalk.co.nz:

The researchers measured heart rate, plasma lactate concentration and creatine kinase. Lactate is produced in the muscles during exercise. At low levels of work the body can metabolize it and so levels in the plasma remain low. As the work level increases the rate of lactate production exceeds the body’s ability to remove it and so concentrations rise. Creatine kinase (CK), an enzyme present in the muscles, is released into the blood as a result of some types of muscle damage.

An animal massage therapist assessed muscle soreness and muscle tightness before and after exercise.

The findings seemed to support the view that horses can carry up to 20% of their body weight without difficulty. There was little difference between all the measures when horses carried either 15% or 20% of body weight. However, when the weight carried increased further, the scientists started to detect differences.

When horses carried 25% or 30% of their body weight their heart rate remained elevated for longer after exercise. The serum CK level was higher immediately after exercise, and 24 and 48 hours later, in horses carrying 30% body weight compared with those carrying 25% or less. There was no change in CK when horses carried 15 and 20%. Plasma lactate levels were higher immediately after exercise and 10 minutes after end of exercise, in horses that carried 30% of their body weight.

The study also investigated whether the horse’s conformation affected its weight-carrying capacity. The scientists looked at the horse’s height, circumference of the cannon midway between knee and fetlock, and width of the back (loin) behind the saddle – between the last rib and pelvis.

They found that horses with wider loins showed less muscle soreness and tightness when carrying 25% and 30% body weight.

Certainly a good starting point, but (at least from what I’ve read) the study doesn’t address such issues as:

• Saddle fit and type: an improperly fitting saddle will cause muscle soreness and tightness regardless of the weight carried.
• Expertise of the rider: we’ve all seen lighter weight riders pound on a horse’s back and seen heavier riders with good balance and a “light seat.” It would be interesting to learn what impact the rider’s ability has on the weight carrying capacity of a horse.
• Breed: Are certain breeds of horses more capable of carrying weight than others?

I don’t think there’s any dispute that we all ride better when we’re fit and trim. And our horses appreciate it, too. Guess I better not put off that New Year’s diet any longer!