Iron is a trace mineral that is required in the horse’s diet. Iron is involved in many bodily processes, including transporting oxygen in the blood and producing energy in cells. [1]

Supplementation with this mineral is usually not recommended because it is naturally abundant in feeds, forages, and even drinking water. Horses are more likely to have excess iron intake than be deficient in this mineral.

Excess iron is not excreted by the body and accumulates in the liver. Over time this can lead to symptoms of iron overload, which is associated with insulin resistance in horses and other animals.

This article summarizes the functions of iron in the horse’s body, nutritional requirements for this mineral, and the link between iron and horse health.

Iron Functions in the Horse’s Body

In the horse’s body, iron is found in many cells and tissues, but it is mostly contained in the muscle, spleen, liver, bone marrow, and blood. [2] The distribution of iron in the body is approximately: [1][2]

  • 60% in hemoglobin, the part of red blood cells that binds to oxygen
  • 20% in myoglobin, an oxygen transport protein found in muscle
  • 20% in proteins, such as ferritin and hemosiderin that store and transport iron
  • 0.2% in enzymes within the mitochondria of cells and elsewhere

Iron is an important component of several enzymes and proteins that are essential for bodily functions. Oxygen transport is one of the most well-studied functions of iron for horses. However, this mineral’s role in diverse processes such as energy metabolism and the immune system are gaining more attention.

Oxygen Transport

Hemoglobin is the protein in red blood cells that binds to oxygen and carries it throughout the body. Each hemoglobin contains four iron atoms with a high binding affinity for oxygen.

When red blood cells pass through the lungs, where there are high levels of oxygen, the iron in hemoglobin quickly binds and captures oxygen.

From there, red blood cells circulate throughout the body, releasing oxygen into areas where the oxygen concentration is lower. [3] Red blood cells then circulate back to the lungs to repeat the process.

It’s important to note that although iron is an critical constituent of red blood cells, supplementing with additional iron will not result in better oxygen carrying capacity of red blood cells. [1]

Cellular Energy Production

Iron is also involved in energy production within all cells by forming iron-sulfur clusters in the mitochondria. Mitochondria are cellular organelles often described as the “powerhouses” of the cell.

In the mitochondria, the iron-sulfur clusters accept electrons and shuttle them along the electron transfer chain. The movement of these electrons generates ATP (adenosine triphosphate), the main energy carrier in cells. [4]

ATP is required for many processes in the body, including muscle contraction, nerve signaling, and protein synthesis.

Immunity

macrophages, which help to protect against pathogens. [2]

Iron is also an important component of the protein lactoferrin, which provides immune support in the mare’s mammary glands and transfers immunity to nursing foals. [2]

In addition to supporting immunity for mares and foals, iron is involved in both innate and adaptive immunity in all life stages of horses.

Innate immunity

The innate immune system is the body’s first line of defense against pathogens. It is non-specific and does not confer any long-lasting protection against a specific pathogen or have a memory component.

The innate immune system includes:

  • Physical barriers (skin, mucus)
  • Chemical barriers (stomach acid)
  • Cellular defenses (macrophages, neutrophils)

As part of the innate immune response, the horse’s body sequesters iron by actively removing it from the bloodstream and storing it within immune cells and storage proteins. The body also reduces iron absorption in the intestine.

This effectively reduces the availability of iron to invading pathogens like bacteria and viruses, which need it to grow and multiply. By restricting access to iron, it prevents the infection from spreading, thereby protecting the horse. [5]

In addition, iron regulates enzymes that produce free radicals, which are used by immune cells to defend against pathogens. [5]

Adaptive immunity

The adaptive immune response is a specialized part of the immune system that develops targeted responses to specific pathogens and retains a memory to provide better protection against future infections.

Although slower to respond, the adaptive immune system confers greater protection by generating antibodies designed to eliminate specific pathogens.

Adaptive immunity involves lymphocytes (B-cells and T-cells) that have the ability to recognize and remember pathogens, providing long-term protection.

In the adaptive immune system, iron is important for replication of lymphocytes. As a mediator of DNA synthesis, iron is critical for allowing B-cells and T-cells to divide quickly, improving the protection against pathogens. [5]