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

Reasons for performing studyAcute, massive enteral carbohydrate overload is associated with laminar inflammation in equids; it is unclear if the same is true for a more prolonged period of moderate dietary carbohydrate intake. ObjectivesTo characterise laminar inflammation in ponies exposed to a dietary carbohydrate challenge meant to mimic acute pasture exposure. Study designIn vivo experiment. MethodsMixed-breed ponies (n = 22) received a diet of hay chop (nonstructural carbohydrate [NSC] approximate to 7% on a dry matter [DM] basis) for 4 weeks prior to initiation of the experimental feeding protocol. Following dietary acclimation, ponies were stratified into either Lean (n = 11, body condition score [BCS] 4) or Obese (n = 11, BCS 7) groups and each group further stratified to either remain on the control, low NSC diet (n = 5 each for Obese and Lean) or receive a high NSC diet (hay chop supplemented with sweet feed and oligofructose, total diet approximate to 42% NSC; n = 6 each for Obese and Lean) for a period of 7 days. Laminar samples were collected following euthanasia and sections stained immunohistochemically for CD163, MAC387/calprotectin and cyclo-oxygenase-2 (COX-2) using commercially available antibodies. The number of CD163 (+) and MAC387(+) cells was quantified for each section; the distribution of COX-2 expression was qualitatively assessed. Laminar mRNA concentrations of several proinflammatory molecules (interleukin-1 [IL-1], IL-6, tumour necrosis factor- [TNF], IL-8, IL-10, monocyte chemoattractant protein-1 [MCP-1], MCP-2), inducible nitric oxide synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), E-selectin, plasminogen activator inhibitor-1 (PAI-1) and COX-2 were evaluated using real-time quantitative polymerase chain reaction (qPCR). ResultsHigh carbohydrate feeding resulted in no increase in laminar proinflammatory cytokine expression; laminar COX-2 expression was increased by high carbohydrate feeding. No laminar leucocyte infiltration was observed in response to high carbohydrate feeding. ConclusionsThese results suggest that the marked laminar inflammation observed in models of sepsis-associated laminitis may not play a central role in the pathophysiology of pasture-associated laminitis.