Plasma concentrations of inflammatory markers in previously laminitic ponies.

Reasons For Performing Study: The mechanisms underlying individual animal predisposition to pasture-associated laminitis remain unclear; however, chronic inflammation is implicated.

Objectives: To identify differences in the inflammatory profile of a group of previously laminitic ponies compared with control animals at pasture in late spring and winter.

Methods: Previously laminitic (PL; n = 38 and 42) and nonlaminitic control ponies (NL; n = 41 and 39) were sampled in late spring and winter. Body condition score, height, weight and crest height and thickness were measured. Plasma concentrations of tumour necrosis factor-α, serum amyloid A, haptoglobin, insulin, adiponectin, triglyceride, fibrinogen, interleukin-17, interleukin-4 and interferon-γ were assayed by validated/standard methods. Factors independently associated with each cytokine were determined by multivariate analysis.

Results: Plasma [adiponectin] was significantly influenced by laminitis status, being lower in PL (median [interquartile range] 2.1[1.4-3.2] μg/l) than in NL ponies (3.4 [2.6-4.1] μg/l; P<0.0001). No other cytokines or inflammatory markers were associated with laminitis status. Plasma fibrinogen and serum amyloid A concentrations were significantly (P = 0.04 and P = 0.01) higher in geldings (3.5 [3.0-4.0] g/l; 2.2 [0.5-3.6] mg/l) than in mares (3.0 [3.0-4.0] g/l; 1.5 [0.4-2.1] mg/l) and significantly (P = 0.04 and P<0.001) higher in winter (3.5 [3.0-4.0] g/l; 2.5 [0.9-3.6] mg/l) than in late spring (3.0 [3.0-3.5] g/l; 1.1 [0.3-1.9] mg/l). Serum haptoglobin concentration showed the same significant (P<0.001) seasonal difference (winter 2.1 [1.6-2.6 g/l; late spring 1.8 1.4-2.4 g/l) and was significantly (P = 0.01) inversely associated with weight. Serum interleukin-4 concentration was significantly (P<0.0001) higher in winter (2.0 [1.2-3.0] ng/l) than in late spring (0.0 [0.0-0.0] ng/l). Serum insulin concentration was significantly (P = 0.02) influenced by season (winter 31.7 [9.6-43.5] miu/l; late spring 84.0 [7.0-131.0] miu/l). Plasma triglyceride concentration was significantly (P = 0.02) higher in PL (0.5 [0.3-0.7] mmol/l) than in NL ponies (0.4 [0.2-0.5] mmol/l).

Conclusions: There were significant effects of season, gender and bodyweight on a number of proinflammatory mediators or markers of inflammation. The only marker influenced by laminitis status was adiponectin, and concentrations of this anti-inflammatory marker were lower in previously laminitic animals.

Potential Relevance: Recurrent laminitis may be associated with reduced anti-inflammatory capacity rather than a proinflammatory state.