Research conducted at Cornell by water-quality expert Dave Beede has been published in the February 
Journal of Dairy Science. In the 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.
Beede also warned that the direct livestock suitability water analysis used by some labs may underestimate the amount of iron in the water as 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.
Conventional nutritional opinion claims that animals do not have the ability to balance their nutritional needs when given the choice. Yet, these researchers relied on the nutritional wisdom of these cows to set their own standards for acceptable levels of iron in their water by providing varying concentration of iron in water "Cafeteria-Style."
Reading between the lines, this experiment also shows that laboratory tests are not as accurate as an animal’s nutritional wisdom --- "some of the iron is chemically associated (bound) with other chemicals in the water and not analyzable." However, when given the choice, the cows didn’t have any problem choosing the level of iron acceptable to them.
And taking that one more step: maybe cows really are smarter than some scientists. Hopefully more researchers will begin to apply common sense in their research and the interpretation thereof.
Keep iron levels in water below 8 mg/L
(DairyHerd.com) 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.
Now, 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.