Iron
To maintain a balanced amount of iron in the body, the body adjusts iron absorption because it has a limited capacity to excrete iron.
The iron present in food can occur as heme iron, which is found in hemoglobin and myoglobin, and as non-heme iron, which is found in plant material.
The absorption of heme iron does not depend strongly on iron status or other nutrients in the diet; however, there are exceptions. Meat increases heme iron absorption, while calcium inhibits both heme and non-heme iron absorption.
Non-heme iron absorption, on the other hand, is strongly influenced by certain nutrients in the diet. The amounts of phytate, tannins, excess calcium, phosphorus, manganese, zinc, copper, and ascorbic acid all affect non-heme iron absorption. Iron status also affects the absorption of this form of iron.
From the above information, it can be concluded that the amount of iron a dog or cat can absorb from its diet depends on the body's iron status, the amounts of heme and non-heme iron in the diet, and the bioavailability of dietary iron, which is strongly influenced by the other nutrients in the diet.
Iron is transported via the plasma and is taken up in the bone marrow. In the bone marrow, iron is then used to synthesize hemoglobin – a protein needed to transport oxygen and carbon dioxide.
The amounts of iron present in urine are negligible. The iron present in feces mainly consists of unabsorbed forms of iron. Iron is also lost through sweat, the nails, and the coat.
Iron is an essential nutrient for dogs and cats because it is present in various enzymes and other proteins responsible for oxygen activation (oxidases and oxygenases), electron transport, and oxygen transport (hemoglobin and myoglobin).
Iron is found in all cells of the body. However, most iron is present as a component of the protein molecules hemoglobin and myoglobin: >65% and approximately 4%, respectively. Hemoglobin is present in red blood cells and is responsible for transporting oxygen. Myoglobin binds oxygen, making it directly available for use by muscle cells. Iron is also a cofactor for various enzymes; without iron, these enzymes cannot perform their functions.
Healthy animals obtain iron exclusively through their diet. The absorption of iron from food, whether heme or non-heme iron, takes place in the duodenum.
The maintenance of iron levels in the body is strictly regulated by the absorption of iron in the intestines, the amount of iron required for erythropoiesis – blood formation –, the recycling of iron from old, aging body cells, and the storage of iron by hepatocytes – liver cells – and macrophages - white blood cells, a type of immune cell in the body.
