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Iron for piglets: Between anaemia and overload

Pig farmers have a responsibility to provide ample amounts of ironfor their piglets. To find out exactly what would be the ideal amount of iron requires some deeperknowledge of a young piglet's physiology. How to define iron anaemia and iron overload?

 
 
Iron plays an important role in health and disease for piglets. Iron is a vital component of the haemoglobin in the erythrocyte (red blood cell) that is the carrier of oxygen in the blood to the tissues. In the farrowing pen, a piglet needs iron for building of tissue and blood. Sow milk does not contain enough iron, so it is important that the piglets have access to an alternative iron source. In the open, the innate rooting behaviour of the piglets will ensure that iron is taken up from the soil, which contains plenty of iron to meet their needs.
 
Therefore, in a modern pig herd, iron must be supplied to the piglets in the form of a supplement to prevent anaemia. But most nutrients are toxic in excess and this is certainly the case with iron.

Iron absorption in the gut
Iron deficiency is the most common nutrient deficiency in humans, and in recent years scientists have clarified many aspects of iron metabolism in humans and animals. These findings may be highly relevant to piglet producers. Dietary iron is absorbed in the proximal intestine by a regulated process that controls body iron homeostasis, since iron excretion is not regulated in mammals.
 
 
Two specialised mechanisms in the mucosal cells help the absorption of iron from the feed (see Figure 1). Divalent metal transporter 1 (DMT1) is responsible of the transport of iron from the gastrointestinal tract into the mucosal cell. When the body iron levels are low, iron is released via ‘ferroportin’ to a carrier in the blood called blood ‘transferrin’, which is responsible for the transport of iron to liver, spleen and bone marrow, where it is stored or used for haemoglobin and erythrocyte synthesis.
 
The regulatory mechanism involves sensing of high body iron levels by the liver which produces an inhibitory hormone hepcidin, that acts on ferroportin in the intestine to decrease iron absorption. Hepcidin also decreases iron export from macrophages that recycle the iron from erythrocytes in the blood and from the storage cells in the liver. This makes hepcidin the key regulator of iron metabolism.Hepcidin also plays an important role in the immune response to infection. The growth of many pathogenic bacteria is inhibited by their inability to scavange adequate amounts of iron from the host. It has been shown that during infection hepcidin will decrease iron absorption in the gut and withhold iron in the macrophages and liver cells making it unavailable to the invading bacteria.

Anaemia and overload
There has been much focus on preventing iron deficiency anaemia but until recently very little on the risk of iron overload. Iron supplementation by an injection of large amounts of iron on day 1-3 is currently the most common practice for the prevention of iron deficiency in piglets. This method bypasses the regulatory mechanism in the gut, and since there is no physiologic mechanism for the excretion of excess iron once it has entered circulation, many piglets suffer from iron overload. From human studies and animal experiments it is well known that iron overload decreases resistance to pathogenic bacteria. Studies have shown that an early iron injection can cause health problems such as polyathritis in piglets.
 
 
 
 
In addition, it is difficult to define when piglets are anaemic. Some veterinarians will say that a piglet is anaemic when haemoglobin levels are below 80 g /l. Others say 100 g/l. Reference ranges for adult pigs are 90-130 g of haemoglobin per litre, but this does not necessarily apply to piglets. Piglets (and other young mammals) undergo major haematological changes in the first weeks of life. For the sow to deliver oxygen to the foetus across the placenta, the oxygen affinity of the foetal blood must be higher than in the sows. The haemoglobin of the newborn piglet gradually changes oxygen affinity towards adult haemoglobin the first weeks after farrowing. Haemoglobin levels of young piglets are therefore probably not comparable to levels of adult pigs.
 

Oral iron – ‘as nature intended’
The best way to prevent anaemia and systemic iron overload at the same time is to provide the piglets with iron orally and for an extended period of time (Figure 2). It is well documented that oral iron powder is superior to other iron products when it comes to work load as well as piglet health. By giving a litter of piglets iron powder orally three times (3 x 40 g) between days 2-4 until the piglets are 10-12 days old, ensures that the piglets have access to iron over a long period. In this way, the piglet can optimise its iron absorption in relation to its individual growth rate and health status.

Biofiber-Damino is a manufacturer of several lines of oral iron products, such as FerkoFer or HemOral.
 

Photo

Tim Hesselballe Hansen, Biofiber-Damino, Denmark

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