A new study has explored how feed restriction, exercise and a combination of the two may affect biological markers associated with inflammation and cartilage turnover in overweight horses.
Equine obesity is linked to serious health concerns, including insulin dysregulation and an increased risk of laminitis. However, carrying excess weight may also affect the body in less visible ways.
Body fat is not simply stored energy. Adipose tissue is biologically active and can release substances involved in inflammatory signalling, potentially influencing tissues throughout the body, including the joints.
Researchers from the University of Guelph investigated whether different weight-management approaches altered selected markers of inflammation and cartilage metabolism in the blood and synovial fluid of overweight horses.
Comparing different management approaches
Following a period during which the horses were brought to an overweight body condition, they were divided into four groups:
- Feed restriction
- Regular exercise
- A combination of feed restriction and exercise
- A control group receiving neither intervention
The intervention continued for ten weeks.
Horses in the exercise groups worked five days each week. Sessions involved 15 minutes of walking, 20 minutes of brisk trotting on the lunge and a 10-minute cool-down.
At the beginning and end of the intervention, the horses also completed a standardised exercise test. Blood and synovial fluid, the lubricating fluid found inside joints—were collected before and at several points after the test.
This allowed the researchers to examine differences between Week 1 and Week 10, alongside the horses’ more immediate biological responses to exercise.
Looking beyond body weight
The researchers measured several biological markers, including prostaglandin E2, nitric oxide and glycosaminoglycans.
Prostaglandin E2, also known as PGE2, is involved in inflammatory processes and has previously been associated with degenerative joint disease when persistently elevated.
Across the horses, synovial-fluid PGE2 concentrations were lower in Week 10 than in Week 1.
This may be considered an encouraging change, but it does not prove that joint inflammation was reduced or that the horses had a lower risk of developing joint disease. The study measured biomarkers rather than clinical outcomes such as joint pain, lameness or osteoarthritis.
Some horses outside the combined feed-restriction and exercise group also lost weight. This may have been influenced by all the horses moving from unrestricted hay during the earlier weight-gain period to more controlled hay provision.
The study therefore cannot establish that one particular intervention directly caused the reduction in PGE2.
What happened in the combined group?
The combination of feed restriction and exercise was the only intervention to produce a statistically significant reduction in body weight. It also had the most marked influence on several of the biomarkers measured.
In Week 10, horses in the combined group had higher nitric oxide concentrations in their synovial fluid than horses in the other three groups. Synovial-fluid glycosaminoglycan concentrations were also higher in the combined group than in the control and feed-restriction groups.
Glycosaminoglycans, commonly shortened to GAGs, are important structural components of cartilage. Changes in their concentrations can indicate that cartilage turnover is occurring, but they do not reveal by themselves whether this represents beneficial adaptation or harmful degradation.
The researchers proposed that the increases in nitric oxide and GAG could reflect adaptive cartilage remodelling following weight loss and repeated mechanical loading.
However, this remains a proposed biological explanation. The study did not directly assess cartilage structure and cannot establish whether the cartilage was protected, repaired or damaged.
Exercise produced an acute biological response
The standardised exercise test produced an acute biological response, including increases in plasma GAG and synovial-fluid nitric oxide at particular sampling points.
Although changes in inflammation-related markers may initially sound concerning, an acute response to exercise does not necessarily indicate lasting damage. Mechanical loading can stimulate normal tissue activity and adaptation.
The timing, size and duration of a biological response are important when interpreting what it may mean.
Synovial-fluid nitric oxide remained elevated at the study’s final 12-hour sampling point. As measurements did not continue beyond this time, the study could not demonstrate exactly when concentrations returned to their pre-exercise level.
It is therefore more accurate to describe this as an acute exercise-related response than to conclude that it was definitively short-lived or fully resolved.
Important limitations
Although the findings are biologically interesting, several limitations must be considered.
The treatment groups were small, containing between six and eight horses. This limits how confidently the results can be applied to the wider horse population.
Mechanical difficulties also meant that one cohort completed its standardised exercise tests on a treadmill, while another was tested on the lunge. Differences in the type or intensity of exercise may have influenced the biological responses recorded.
The horses had also become overweight relatively recently as part of the research programme. Their responses may not represent those of horses that have been overweight or obese for several years.
In addition, the horses were not explicitly tested for equine metabolic syndrome or pituitary pars intermedia dysfunction, commonly known as PPID. These conditions may affect metabolism, inflammation and approaches to weight management.
Most importantly, biomarkers can provide information about biological activity, but they cannot show on their own whether a horse’s joint health has clinically improved or deteriorated.
Further research involving larger groups of naturally and chronically overweight horses would be needed to determine whether these changes have meaningful, long-term effects on cartilage and joint health.
What does this mean for horse owners?
The study found that feed restriction and exercise were associated with changes in markers linked to inflammation and cartilage turnover in overweight horses.
The combined approach produced the only statistically significant reduction in body weight and the clearest differences in several biomarkers. However, this does not prove that combining feed restriction and exercise protects cartilage or prevents osteoarthritis.
Some of the findings could be consistent with adaptive cartilage remodelling in response to weight loss and mechanical loading, as proposed by the researchers. Other interpretations cannot be ruled out based on the measurements taken.
The study supports the wider importance of maintaining a healthy body condition, but it does not identify a single weight-management programme suitable for every horse.
Weight loss must be approached carefully. Inappropriate feed restriction can compromise digestive health, nutritional balance and welfare, while exercise should be suitable for the horse’s fitness, soundness and metabolic health.
Owners concerned about their horse’s weight should seek advice from their vet and a suitably qualified equine nutrition professional before making substantial changes to their horse’s diet or exercise programme.
The findings are encouraging enough to support further investigation—but they should not yet be presented as evidence that diet and exercise directly improve or protect equine joints.
