Laminar inflammatory events in lean and obese ponies subjected to high carbohydrate feeding: Implications for pasture-associated laminitis.

This study investigates the effects of high carbohydrate feeding in both lean and obese ponies to understand its implications for a horse condition known as pasture-associated laminitis. The research finds that while high carbohydrate feeding increases the expression of a particular enzyme (COX-2), it does not significantly increase other proinflammatory markers or cause immune cell infiltration in the laminae (layers of hoof tissue), suggesting a different underlying mechanism for pasture-associated laminitis than for sepsis-associated laminitis.

Research Objective and Methodology

The main aim of this study was to investigate the impacts of high carbohydrate diets on the development of inflammation in the laminar tissue of ponies’ hooves, a condition linked to a form of laminitis associated with pasture feeding. The researchers compared the effects of this diet in both lean and obese ponies over a seven-day period.

• The researchers selected 22 mixed-breed ponies that had been acclimatized to a low-carbohydrate diet for four weeks.
• The ponies were divided into two groups: Lean (with a body condition score (BCS) ≤4) and Obese (BCS ≥7). Each of these groups was further subdivided into those that remained on the low-carbohydrate diet and those that switched to the high carbohydrate diet.
• At the end of the experimental feeding protocol, the ponies were euthanized and their laminar samples collected.

Laminar Inflammation Characterization

To determine whether high carbohydrate feeding resulted in laminar inflammation, the researchers identified and quantified several markers:

• They used immunohistochemical staining on the laminar sections for CD163, MAC387/calprotectin, and cyclo-oxygenase-2 (COX-2), markers that are commonly associated with inflammation.
• The number of CD163(+) and MAC387(+) cells was counted.
• The distribution of COX-2 expression was qualitatively assessed.
• They also evaluated the concentration of several pro-inflammatory molecules (such as various interleukins, and tumour necrosis factor-α), inducible nitric oxide synthase, intercellular adhesion molecule-1, E-selectin, plasminogen activator inhibitor-1, and COX-2 mRNA in the laminar tissue.

Findings and Conclusion

The researchers found that high carbohydrate feeding in ponies did not increase the expression of proinflammatory cytokines, suggesting that high carbohydrate feeding does not trigger the same inflammatory response commonly observed in sepsis-associated laminitis. However, it did increase COX-2 expression in the laminar tissue. There were also no signs of immune cell infiltration in response to a high carbohydrate diet.

These findings could have significant implications for understanding the underlying mechanisms of pasture-associated laminitis. From these results, the researchers concluded that the prominent laminar inflammation seen in sepsis-associated laminitis may not play a central role in the pathophysiology of pasture-associated laminitis. This suggests that further research is needed to fully understand the mechanisms of different forms of laminitis.