Iron is an essential component of the proteins involved in oxygen transport or utilization. These proteins, including hemoglobin, myoglobin and a number of cytochrome and iron-sulphur proteins, are involved in the electron transport chain. Several mammalian enzymes also either contain or are activated by iron. More than 50 % of the body’s iron is present in hemoglobin; smaller amounts are present in other iron requiring proteins, enzymes and in protein-bound stored iron. Most practical feedstuffs have more than adequate amounts of iron, and iron deficiency is unlikely in animals. In most field conditions, the iron deficiency is a secondary one due to either protein deficiency or parasite infestations or diseases causing chronic blood loss. Without blood loss, only small amounts of iron are lost through urine and feces.
Cereal grains normally contain 30 to 60 mg Fe/kg; oilseed meals contain 100 to 200 mg Fe/kg. With the exception of milk and milk products, feeds of animal origin are high in iron: meat and fish meal contain 400 to 500 mg Fe/kg: blood meal usually has more than 3,000 mg Fe/kg. Although the iron content of forages is highly variable, most forages contain from 70 to 500 mg Fe/kg. Much of the iron variation in forage is likely caused by soil contamination. Water and soil ingestion can be significant sources of iron for livestock, although availability from forages appears to be lower than other sup plementa l ir on sourc e s. I nc re asing dietar y ca lcium a nd /or p ho sp ho rus concentrations decrease iron absorption. Citrate, fumarate and gluconate forms of iron have been found to be equal in bioavailability to that of ferrous sulphate