Researchers investigate cause of insulin response in equine metabolic syndrome

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PhD student Erica L. Macon. © University of Kentucky

A research team at the University of Kentucky is working on a study to learn if additional starch or sugar in a horse’s diet is the main driver for the insulin response seen in Equine Metabolic Syndrome (EMS).

EMS is composed of three characteristics. Firstly the consistent feature of EMS animals is that they demonstrate insulin dysregulation (ID), a collective term for both tissue insulin resistance and basal/postprandial hyperinsulinemia. This means that typically the concentrations of insulin in the blood are higher than what’s considered normal either before and/or after eating feeds and forages especially those rich in starch and/or sugar.

Secondly, there is an increased risk of developing endocrinopathic laminitis, which is laminitis resulting from hormonal (in particular insulin) disturbances rather than in association for example with severe infection (sepsis) or certain intestinal conditions.

Finally, most, but not all, EMS animals show increased general or regional adiposity meaning that many are overweight or more typically obese.

The main risk factor for endocrinopathic laminitis is now believed to be insulin dysregulation although the exact link between abnormally high circulating insulin concentrations and the development of laminitis is not known.

But it does mean that what horses are fed may directly impact their risk for endocrinopathic laminitis.

Erica Macon, a PhD student at the Gluck Equine Research Center, said that limited work has been undertaken in the EMS/ID horse and current recommendations were largely derived from horses that suffered from polysaccharide storage myopathy (PSSM), a very different condition.

“Thus, we set out to explore and, help define nutritional recommendations for EMS/ID horses and thereby improve their welfare.”

The team’s first look at the topic was carried out in collaboration with Pat Harris, head of the Equine Studies group at the Waltham Petcare Science Institute. They fed various feedstuffs to EMS/ID horses as well as healthy horses in two separate studies.

Their study, Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non-insulin dysregulated controls, was published in the Equine Veterinary Journal.

Currently, it is typically recommended that EMS/ID horses are fed low sugar and starch feeds and forages that contain <10-12% non-structural carbohydrates (NSC, ie, starch and water-soluble carbohydrates) on a dry matter basis with an appropriate ration balancer. In the first study, various feeds with different levels of protein and NSC were fed in a cross-over study to both ID and non-ID horses.

The results of this study showed that even when fed low amounts (~1g/kg BW) of certain feeds that did not provoke any insulin response in Non ID horses, exaggerated insulin responses may occur in ID animals, confirming the need to undertake work specifically in such individuals.

In addition, the study suggested that non-structural carbohydrates were the main driver behind the post-meal insulin response rather than protein in the ID horse. In the second study, the team fed diets with a range of NSC contents and showed that under these conditions the threshold for the exaggerated insulin response in ID horses appeared to be between 6-15% NSC  on a dry matter basis.

The follow-up study is looking to identify the main driver for the insulin response and further define where the likely NSC threshold range may be when fed such simple diets.

Macon, who works in the laboratory of associate professor Amanda Adams at Gluck, said the team was composed of equine enthusiasts and is dedicated to improving the understanding of this endocrine disorder and the welfare of EMS/ID horse.

“When combined with other work showing the potential effects of other nutrients on the insulin response, such as oil inclusion, these results should help with the development of rations that decrease the risk of endocrinopathic laminitis,” Macon said.

The work has been funded by Mars Horsecare and The Waltham Petcare Science Institute.

Article courtesy University of Kentucky College of Agriculture, Food and Environment.

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