At the Cornell Nutrition Conference last October, water-quality expert Dave Beede offered a sneak peek into research on iron concentrations in the drinking water of dairy cattle.

Keep iron levels in water below 8 mg/LNow, the research has been published in the February Journal of Dairy Science.

In an experiment, Beede and other researchers set up a series of water tubs cafeteria-style, so they could see which tubs the cows preferred based on iron concentrations in the water. Upon first exposure to drinking water, lactating dairy cows tolerated iron concentrations up to 4 mg/L (or 4 parts per million) without a reduction in water intake; however, water intake was reduced with concentrations of 8 mg/L.

Here’s an additional caution: The direct livestock suitability water analysis used by some labs may underestimate the amount of iron in the water. In the “direct method,” some of the iron is chemically associated (bound) with other chemicals in the water and not analyzable. Therefore, what may appear as a favorable 2 mg/L level may actually be an inhibitory 8 mg/L level. So, when working with a reference laboratory, be sure to ask for the “acidification method” which determines total recoverable iron. With the acidification method, the water sample is acidified first with nitric acid before analysis, and this acidification makes all of the iron available for analysis.

“I recommend that the lab be called to ensure that the acidification step is done before iron analysis,” Beede says.