Researchers Identify Link between Insulin Resistance, Iron Overload
Insulin resistance (IR), in which cells fail to respond normally to the hormone insulin, is becoming increasingly recognized in horses. Although several factors have been linked with IR onset in horses, researchers now speculate that elevated iron (ferritin) levels could be a significant risk factor.

Researchers from Michigan State University (MSU) recently performed a study to explore the link between IR and iron overload in captive rhinoceroses; however, the team used horses, which have a similar digestive tract to rhinos, as a model for practical reasons (rhinos aren’t the easiest animals to work with). They aimed to determine if an association between high ferritin concentrations (indicative of iron stores in the body) and insulin resistance exists in horses.

The team employed 15 healthy horses and one IR horse and fed them a grass hay diet with no concentrates. All horses were administered two treatments after a 12-hour fast:

  • Dextrose, a form of glucose, administered at 0.25 g/ kg of body weight; and
  • Pelleted corn at 1.5 g/kg of body weight.

The team analyzed blood insulin levels just before and every 30 minutes (up to two hours) after treatments. They also evaluated ferritin levels and found concentrations ranging from 130-882 ng/mL. Lead researcher and professor at MSU’s Department of Animal Science, Brian Nielsen, MS, PhD, PAS, Dipl. ACAN, said previous research suggests that normal adult serum ferritin is 180-210 ng/mL.

Other key findings in the study include:

  • Ferritin was positively correlated with peak insulin and insulin AUC (area under the curve, or the length of time insulin and glucose stay elevated);
  • The most significant correlation was found between ferritin and insulin AUC after dextrose administration;
  • Female horses showed a stronger correlation between ferritin and insulin AUC than male horses; and
  • The IR horse had the highest serum ferritin concentration and the highest insulin response.

Based on these results, Nielsen relayed, “If (a horse is) overweight and is not given sufficient exercise, then it might warrant trying to give feedstuffs lower in iron or, more importantly, not giving them as much feed or feed of higher quality.”

Pertaining to future studies in this area, Nielsen added, “A goal of my research program is to answer questions in which people have interest, so maybe we will have to look at this (issue) more closely.”

The study, “A potential link between insulin resistance and iron overload disorder in browsing rhinoceroses investigated through the use of an equine model,” was published in Journal of Zoo and Wildlife Medicine in 2012.