Answer provided by Dave Beede, professor of dairy nutrition, nutrient and environmental management at Michigan State University.
Q: How much iron are your clients supplying to cows through the drinking water each day?
A: Hopefully, not too much! Excess iron in water causes iron toxicity and is a major problem in some dairies across the country. In this time of high input costs, excess iron and subsequent poor cow performance can be the business-breaker. Fortunately, excess iron in drinking water is relatively easy to detect with a standard laboratory analysis. Then corrective action can be taken.
The recommended maximum tolerable concentration of iron in drinking water is 0.3 ppm (parts per million). Concentrations in excess of this can be a major detriment to normal health and performance of dairy cows, and a significant health risk for humans. A cow producing 100 pounds of milk requires about 35 milligrams of absorbed iron daily, commonly supplied in her ration. However, if she consumes drinking water with 0.3 ppm iron (versus no iron in water) her total absorbable iron intake doubles. If the drinking water contains 0.6 ppm iron, then total absorbable iron intake is three-fold the dietary requirement. I’ve seen many laboratory analyses of drinking water from dairies where iron concentrations are 1, 2, 3,……even as high as 8 ppm.
Typically, in most rations there is plenty of total iron to meet the cow’s absorbed iron requirement, even though dietary iron is very insoluble in the digestive tract of adult cattle and only about 10 percent absorbable. The common chemical form in feeds is ferric iron, Fe+3. In contrast, iron in drinking water is highly soluble and nearly 100 percent absorbable (ferrous iron, Fe+2). So, major problems result from high iron in water.
Excess iron in drinking water can lead to cellular oxidative stress and inhibit copper and zinc absorption. Oxidative stress results in damage to cell membranes and disrupts normal physiological functions and biochemical reactions. It is suspected that consequences of excess iron and heightened oxidative stress are magnified in transition and fresh cows with compromised immune function, increased fresh cow mastitis and metritis (excess ferrous iron in the body enhances the potential for bacterial infections), greater incidence of retained placentas, diarrhea, below normal feed intake, and reduced growth and milk production.
To my knowledge, there are no controlled research studies quantifying animal responses to excess iron in drinking water or removal of that iron. Nonetheless, anecdotal evidence from several field cases in the last several years suggests marked improvements in milk yield and cow health when excess iron is removed from drinking water.