Obesity and its related health issues remain a problem in both horses and humans. Researchers have linked obesity—specifically adipose (fat) tissue—with excessive inflammation biomarker production, but they haven’t yet found a correlation between obesity and degenerative joint diseases, such as osteoarthritis.

So Wendy Pearson, MS, PhD, of the University of Guelph, in Ontario, Canada, and the Nutraceutical Alliance, set out to determine if there’s a link between body fat, horse activity level, and inflammatory biomarkers, specifically prostaglandin E₂ (PGE_2, which is associated with synovial, or joint, inflammation and cartilage matrix depletion) and glycosaminoglycan (GAG, an important joint cartilage component).

The team studied 54 horses residing on private farms in Southern Ontario. They estimated the horses’ body weights and body condition scores (BCS), then categorized horses as thin (a BCS of 3 out of 9, six horses), moderate (BCS of 4 or 5, 18 horses), overweight (BCS of 6 or 7, 19 horses), or obese (BCS=8 or 9, 11 horses). The researchers measured the horses’ body fat mass and body fat percentage and recorded the owner-reported activity level (nonvoluntary, forced exercise). Finally, they collected joint fluid from horses’ knees as well as blood samples to test for PGE₂ and GAG concentrations.

Not surprisingly, compared to thin horses, obese horses weighed more and had greater body fat mass and percentage. However, they also had higher plasma PGE₂ concentrations. There were no differences between the groups’ joint fluid GAG or PGE₂ concentrations.

Additionally, the researchers found that horses’ lameness scores correlated slightly with body fat mass—this means horses carrying more body fat were a little more likely to be lame than their leaner counterparts.

Finally, they found that activity level appears to influence BCS and might possibly play a role in the correlation between BCS and plasma PGE_2. Essentially, horses that have higher activity levels could have lower a BCS, and horses with lower BCS might have lower plasma PGE₂ concentrations. The researchers noted that these results should be “interpreted with care” due to the small sample size and limited number of “thin” horses.

The Bottom Line

Scientists are still working to fully characterize the relationship between obesity and degenerative joint diseases such as osteoarthritis. But Pearson and colleagues did determine that horses’ body weight, BCS, and body fat percentage and mass appear to be correlated with blood concentrations of PGE₂—a potential joint damage marker. The team noted that further studies will need to clarify the source of these inflammatory biomarkers, plus identify others that might be involved.

The study, “Exploring relationships between body condition score, body fat, activity level and inflammatory biomarkers,” was published in the Journal of Animal Physiology and Animal Nutrition.