Unfortunately, we don’t know the upper threshold at which iron in drinking water is likely to be a problem. Recommended maximum tolerable concentration generally listed by analytical laboratories is 0.3 ppm. This apparently was derived as an acceptable level for palatability in humans. However, the actionable negative iron threshold in drinking water for dairy cattle is unknown. Typically, in most rations plenty of iron is present to meet cows’ requirement, even though the form of iron (ferric: Fe+3) is only about 10% absorbable. In contrast, iron (ferrous: Fe+2) in drinking water is highly soluble and presumed to be nearly 100% absorbable, probably increasing the risk for problems.
Experience in field cases in the last several years suggests improvements in milk yield and cow health when excess iron is removed from drinking water or a different water source with low iron is used.
Fortunately, excess iron in drinking water is relatively easy to detect with a standard laboratory analysis and corrective action can then be taken relatively easily. Options are:
- find a different drinking water source with lower iron; or,
- treat drinking water to oxidize ferrous iron to ferric and then remove it from the system by filtration.
The simplest way to oxidize ferrous iron is by exposure to air (oxygen) such as with an ‘iron curtain’. Cost-effective water treatments include hydrogen peroxide or chlorination to oxidize ferrous iron to ferric iron followed by mechanical filtration. Other methods (such as ozonation, reverse osmosis, or an oxidizing filter) or really fancy water treatment systems can react and remove iron also, but careful assessment of installation and operating costs are very highly recommended. These guidelines on how to take a drinking water sample and standard water analysis can help.