Chemical properties and distribution

Most iron is in complex forms bound to protein as

• Porphyrin (or heme) – particularly hemoglobin and myoglobin
• Nonheme protein-bound complexes, e.g transferrin, ferritin and hemosiderin

Metabolism

Absorption and transport

Limited capacity to excrete iron, homeostasis largely controlled by absorption.

Absorption of iron is affected by:

• age, iron status and state of health
• conditions within the gastro-intestinal tract
• amount and chemical form of iron
• amounts and proportions of other minerals and compounds

High dietary phosphorous can reduce iron absorption

Iron is transported in the body via transferrin, transferrin accepts iron from absorption, from sites of storage and hemoglobin. Transferrin delivers iron to the bone marrow (for hemoglobin synthesis), to the placenta and to cells for iron containing enzymes.
Placental iron transport with the horse is unidirectional and increases rapidly as pregnancy progresses. Hemoglobin iron conservation is achieved by cells in the liver, spleen and bone marrow that recruit iron erythrocytes. Released iron is rapidly returned to the circulation (e.g, transferrin).

Storage

A horses iron status is reflected by the concentration of ferritin and hemosiderin. The liver contains approx 60% of ferritin, approx 40% is stored in muscle and cells of the reticuloendothelial system. Normally 95% of iron is stored in the liver as ferritin, 5% is stored as hemosiderin. The storage of iron in newborns is influenced by the maternal diet, most storage is late in gestation.

Physiological functions

• Role in many biochemical reactions including: oxygen transport, the electron transport chain, the citric acid cycle, and ribonucleotide reductase
• Enzymes for electron transport, activation of oxygen and for oxygen transport
• Iron is in the body as:
  - Heme cpds – hemoglobin or myoglobin
  - Heme enzymes – mitochondrial and microsomal cytochomes, catalase and peroxidase
  - Nonheme cpds – flavin iron enzymes, transferrin and ferritin

Requirements

Requirements for a horse is made difficult by individual variation in absorptive capacity and bioavailability among foods. Copper and manganese can compete with iron for absorption sites.

Deficiency

• Microcytic, hypochromic anemia
• Difficult breathing (e.g racing or work horses)
• Poor growth, scouring, pneumonia, more susceptible to disease, rough hair coat, lack of healthy colour, blood looks watery

Deficiency is generally not a problem unless horses are heavily parasitised.

Assessment of iron status

Hypochromic, microcytic anemia (RBCs small with less hemoglobin), iron in plasma-bound transferrin is reduced.