Fat Horses, Laminitis Risk Linked

Equine metabolic syndrome (EMS) in horses is characterized by obesity, insulin resistance and laminitis. Two experiments were done with horses affected by EMS and normal controls to better understand why EMS is linked to laminitis.

First the inflammatory response to endotoxemia was compared between six horses naturally affected by EMS and six normal controls. Insulin and glucose dynamics were measured and also compared between EMA and normal horses. An infusion of lipopolysaccharide was used to create the endotoxemia under controlled conditions and serial blood samples were obtained over several hours.

Temperature, heart and respiratory rates increased in all horses following the initiation of the endotoxemia. Gene expression of several cytokines (signaling molecules that affect the immune system and inflammation) also increased. The blood levels of these chemical messengers (interleukins and tumor necrosis factor) did not increase, but the gene expression was prolonged in EMS horses.

Insulin sensitivity was decreased in all horses following the endotoxemia event. This effect was greater and lasted longer in EMS-affected horses.

These results help explain why EMS (and obese) horses tend to be at greater risk for laminitis and more severe or prolonged bouts of laminitis compared to healthy horses. The authors also suggest that EMS horses may be predisposed to laminitis following insulin-glucose derangements caused by stress, but how this follows is not entirely clear.

— Tadros EM et al. AJVR 2013;74:1010-1019 and 020-1029.

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