Iron requirements in animals

Iron has been recognized as a required nutrient for animals for more than 100 years (Pond et al., 1995). Still, sub-clinical iron deficiencies occur more frequently than recognized by most livestock producers. Currently, micronutrient deficiency is a bigger problem than macronutrient deficiency, because the farmer does not readily see specific symptoms that are characteristic of a trace mineral deficiency. Instead, the animal grows or reproduces at a reduced rate, uses feed less efficiently and operates with a depressed immune system (Berger, 2000). Both iron deficiency and iron excess can compromise the immune system of farm animals. Hypoferremia is believed to be an important protective component of the acute phase response to infection (Ebersole and Capelli, 2000). It is proposed that the decrease in red blood cells, in the acute phase following infection and inflammatory disease, is a strategy to decrease iron availability to pathogens (Ebersole and Capelli, 2000). On the other hand, anemic animals are much more susceptible to infections than those with adequate iron. Nursing pigs made anemic by withholding supplemental iron for four weeks after birth were more susceptible to the lethal action of bacterial endotoxin then their littermates that had been given iron (Osborn and Davis, 1968). Once the infection was established, iron supplementation increased the bactericidal activity of liver and splenic macrophages. In another example, chicks inoculated with Salmonella gallinarum had increased survival when iron (100 ^g/g of diet or more) was added to a basal diet containing 200 ^g/g of iron (Hill et al., 1977; Smith et al., 1977). These and other data in broilers show that iron helps the immune system to destroy the invading organism. Therefore, proper iron nutrition is essential for maximal disease resistance.

Table 1-2. Dietary iron requirements (mg/kg of diet dry matter) in different animal classes (adapted from NRC 1981, NRC 1985, NRC 1989, NRC 1994, NRC 1996, NRC 1998, NRC 2001). _

Class of Animal

Iron Requirements (mg/kg of diet dry matter)

Swine

Piglets

100

Growing-finishing

40 - 80

Dairy cattle

Calves

100

Other cattle

25

Beef cattle

50

Sheep

30 - 50

Goats

30 - 50

Horses

40 - 50

Poultry

50 - 80

Several factors influence the iron nutritional status and/or iron needs of animals. These include: 1) genetic differences amongst species, breeds, strains, stocks, sexes or individuals, 2) life cycle stage, with special emphasis on growth, pregnancy and lactation, 3) health status of the animal, 4) form of iron used in the diet (e.g. type of chelator), and 5) nutritional and anti-nutritional factors taken together with the iron source (NRC, 1989). Although there are minimally established nutrient needs for animals, designed to minimize the risk for deficiency, farm animals are usually fed to maximize their mass and/or to increase production in terms of meat, eggs, or milk (Grusak and Cakmak, 2005). Thus, mineral recommendations for production purposes are usually higher than those to prevent deficiency. Table 1-2 gives the feed iron recommendations for different classes of animals at different growth stages. When there is a range of requirements for the same animal class, the higher value corresponds to the animal at a younger growth stage, or to females during pregnancy or lactation. The values for feed composition recommendations range from 25 mg/kg for adult dairy cattle up to 100 mg/kg for piglets or calves.

Table 1-3. Iron (mg) content of selected plant foods, raw, per common measure and per 100 g FW basis. Adapted from USDA National Nutrient Database for Standard Reference, Release 17, 2004._

Description

Common

Iron content (mg)

measure

Per common measure Per 100 g FW basis

Fruit

Apple

1 apple

0.17

0.12

Avocado

1 oz

0.17

0.60

Banana

1 banana

0.31

0.26

Nectarine

1 nectarine

0.38

0.28

Strawberry

1 cup

0.70

0.42

Legumes

Black Bean

1 cup, cooked

3.61

2.10

Chickpea

1 cup, cooked

4.74

2.89

Lentil

1 cup, cooked

6.59

3.33

Vegetables

Cabbage

1 cup

0.41

0.58

Carrot

1 cup

0.33

0.30

Lettuce

1 cup

0.23

0.42

Potato

1 potato

2.18

1.10

Spinach

1 cup

0.81

2.70

Tomato

1 tomato

0.33

0.26

Nuts

Almond

1 oz (24 nuts)

1.22

4.30

Cashew

1 oz (18 nuts)

1.72

6.06

Cereal Grains

Barley

1 cup, cooked

2.09

1.33

White Rice

1 cup, cooked

0.24

0.14

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