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Iron: Friend or Foe?

March 2017 by Jenene Redding, BVSc (Hons),

Iron has been the subject of much discussion, mainly regarding its possible role in the development of Insulin Resistance (IR) in horses.

This idea stemmed from research performed by the Michigan State University where they explored a potential link between IR and iron overload in black rhinoceros held in captivity (Nielsen, Vick & Dennis 2012), a disorder which hasn’t been documented in the wild. 

The study used equine models as they have a similar digestive system to rhinos. The goal of the research was to determine whether iron accumulation in rhinos was a result of them being IR or whether rhinos were developing IR from the overconsumption of iron.

During the study, researchers identified a correlation between IR and elevated serum ferritin levels, leading some to believe iron overconsumption was leading to IR. 

In 2013, this question was put to the lead researcher Brian D Nielsen, Ph.D., PAS, Dipl. ACAN, and this was his response: “Most captive rhinos are overweight (similar to horses) and likely do not receive adequate exercise (again similar to horses).” 

To begin lessening the symptoms of IR, he first suggested addressing the factors that caused the horse to become insulin resistant in the first place i.e. reduce weight and increase levels of exercise and, by correcting these factors, iron in the diet was likely to be a non-issue. 

He then states: “There is no good evidence to suggest that feeding a diet low in iron can correct insulin resistance or that feeding a diet containing excessive iron contributes to insulin resistance in the first place”.

So, what is the function of iron?

Iron is essential for the transport of oxygen in the body. Without it, animals die. Because iron is essential, the body has become very effective at scavenging and storing iron from the breakdown of red blood cells.

The properties of iron allow it to donate and accept electrons as an integral part of its function. This means it can catalyse free radicals that potentially damage and destroy cells. To prevent cell damage, all life forms that use iron, bind it to proteins. 

This allows living organisms to benefit from iron, while limiting its ability to do harm. Free iron is typically less than 5% of total cellular iron.

One of the body’s defence mechanisms against bacterial infections is to control levels of iron. In chronic, long-term inflammatory conditions, such as Equine Metabolic Syndrome, Cushing’s, Laminitis, Gastric Ulcers, the circulation of iron is limited by the body, leading to increased storage and reduced absorption.

Body levels of iron are usually the result of a controlled rate of absorption via the digestive system and uncontrolled losses are the result of cellular loss, sweat, injuries, lactation and blood loss. As such, absorption of dietary iron is variable.

Iron is absorbed by specialised protein molecules from the gut and transported as ferrous iron into the cell. These cells can store iron as ferritin, which is then lost in faeces when the cell dies. When required, ferritin can be released from the cell into the body.

Hepcidin is a liver enzyme that controls the release of iron from intestinal cells. In a normally functioning individual, excess iron cannot be absorbed.

Injectable iron supplements are far more likely to result in iron toxicity as the control mechanisms in the digestive system are bypassed.

It is reasonable to assert horses that have developed IR are those whose physiology is less able to adapt to modern feeding and exercise regimes. Horses evolved roaming vast areas, consuming large amounts of poor quality roughage. 

In nearly all IR cases in horses, the common underlying factor is an excessive intake of carbohydrates, combined with inadequate exercise. 

In the 1990’s, Dr Lex Wills, BVSc (Hons) MACVSc, developer of Equilibrium and the Equilibrium Feeding Program, realised horses being fed diets rich in concentrates, combined with inadequate exercise regimes, were suffering compromised health. 

The Equilibrium Feeding Program has always stressed the importance of bulk roughage feeding with the addition of Equilibrium Mineral Mix or B1 Cool Mix to provide and balance the mineral and vitamin requirements of horses. Simple, safe, effective and economical.

For further information on iron and other minerals, visit: