Aust researchers delve into inflammation-insulin dysregulation link in horses

Inflammation may be a bigger player in insulin dysregulation in horses than is commonly thought.
Inflammation may be a bigger player in insulin dysregulation in horses than is commonly thought. Morris Animal Foundation-funded researchers at the University of Melbourne in Australia are working to determine if low-grade systemic inflammation might be an important underlying cause of insulin dysregulation. © Dr Simon Bailey, University of Melbourne

Researchers in Australia are working to determine if low-grade systemic inflammation might be an important underlying cause of insulin dysregulation.

A new study at the University of Melbourne funded by the Morris Animal Foundation aims to learn just how much of a role inflammation plays in insulin dysregulation in horses. Their findings could help change current dietary recommendations for horses at risk of laminitis, a devastating disease linked to high insulin levels associated with insulin dysregulation.

“While there’s evidence to support this theory, recent studies infer we do not understand exactly how different diets cause changes in insulin metabolism,” said University of Melbourne lecturer Dr Nicholas Bamford. “We want to investigate other possibilities to provide horse owners, veterinarians and feed manufacturers with the best information to keep horses healthy.”

Insulin dysregulation is a condition that occurs when horses produce excessive amounts of this hormone in order to process blood glucose. The current recommendation for feeding horses with the condition is to avoid high-starch and high-sugar diets. As insulin is released by the pancreas in response to dietary starches and sugars, reducing the amount of these components in the diet would theoretically reduce the amount of insulin secreted following a meal.

In the new study, Bamford’s team will analyse archived blood samples from 49 horses from previous diet studies, conducted at the University of Melbourne and University of Minnesota, to measure their levels of adiponectin and serum amyloid A (SAA). Adiponectin is a fat-derived hormone known to have beneficial effects on insulin metabolism, as well as being anti-inflammatory. Reduced levels of adiponectin have been demonstrated in horses with insulin dysregulation. Serum amyloid A is a marker of systemic inflammation thought to be the most sensitive in horses with insulin dysregulation.

The team hypothesizes that one of the significant causes of insulin dysregulation in long-term, starch-fed horses results from low-grade systemic inflammation, a mechanism that has been found in other species. Obesity can cause a chronic pro-inflammatory state in other species, but Bamford said this does not appear to be the case in horses.

In previous studies, horses were fed either a high-sugar or high-starch diet for seven or 20 weeks. Horses in the group that were fed a high-starch diet for 20 weeks demonstrated insulin resistance, as well as decreases in adiponectin and increases in SAA, whereas those on other high-calorie diets did not develop insulin resistance (even if they became obese). Adiponectin and SAA were not measured in every group, though, so it is unclear how levels of these analytes changed over time. Bamford’s team will address this question. He estimates they will have the results in about a year.

Morris Animal Foundation Chief Scientific Officer Dr Janet Patterson-Kane said that determining the causes of insulin dysregulation, and why certain horses appear to be predisposed to it, is important for equine populations. “This knowledge could provide an important contribution to the development of nutritional countermeasures to help reduce the incidence of laminitis.”

Underlying insulin dysregulation has been shown to account for about 90% of all laminitis cases in some populations. Laminitis is a painful and debilitating inflammation of tissue in a horse’s hooves, causing severe lameness. It is one of the leading causes of death or euthanasia among domestic equine populations.

Studies have shown that as many as 15% of horse owners reported problems with laminitis in their horses over the previous 12 months, with about 5% of cases resulting in death or euthanasia. There is currently no effective treatment for laminitis, so prevention is crucial to avoid its occurrence in susceptible horses.

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