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Assessing appropriate iron levels in drinking water for cows

Stephanie Skernivitz Published on 31 October 2013

When given access to drinking water, lactating dairy cows can handle iron (Fe) concentrations of up to 4 parts per million (ppm) without decreasing the amount of water they consume, according to results of a recent study entitled, “Preference and drinking behavior of lactating dairy cows offered water with different concentrations, valences and sources of iron.”

Additionally, results showed that cows did not drink as much water if total recoverable iron concentration was 8 ppm. Researchers also noted that the cows did not markedly discriminate against water that differed in Fe valence or Fe from different chemical sources.

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The current recommendation for acceptable levels of Fe in drinking water is 0.3 ppm or less, but this is based on guidance for human preference. Yet research suggests that cattle may be able to function normally with somewhat greater concentrations of Fe.

A significant note, according to study author Dr. Dave Beede, professor of dairy management and nutrition at Michigan State University, is that “the 0.3 ppm or less iron concentration listed as the maximum contaminant level published in most water quality tables (and water analysis laboratory reports) is from EPA’s recommendation of the concentration thought to affect palatability (taste) of drinking water for humans; it really has nothing to do with dairy cows.”

Beede says this is “a very important point” for dairy producers and nutritionists to know, so they do not “overreact” to concentrations somewhat above 0.3 ppm (such as 1 or 2 ppm iron) where there most likely is no water quality problem affecting cows.

Such “overreaction” may lead to installing a water treatment system to remove low concentrations of iron when it actually does not make any difference in cow health or productivity and will end up costing money unnecessarily.

He adds that to date he’s not aware of research results or field experience to support any nutritional or management actions at less than 2 ppm iron.

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According to Beede, evaluating acceptable iron levels for palatability of water by lactating dairy cows is just one focal point of the recent study, published in February 2013 in the Journal of Dairy Science .

Researchers for this paper, led by Beede and Olivia Genther, a MSU graduate student who conducted the study, sought to assess the impact of different amounts of ferrous Fe2+ or ferric Fe3+ iron and Fe sources on how lactating dairy cows consumed water.

“The scope of our published study is limited and only addresses one aspect of drinking water nutrition and quality – that is, the palatability or preference and intake by lactating cows of drinking water with different concentrations, valences and sources of iron.

The research does not evaluate any of the potential post-absorptive effects or aspects of iron on lactational performance or health of dairy cows,” Beede says.

The authors conducted four cafeteria-style experiments in which cows were given water treatment pairs for 22-hour durations. During this time, water consumption and drinking behavior were monitored.

The first experiment offered 0, 4 or 8 ppm of total recoverable Fe from ferrous lactate mixed into drinking water. As indicated previously here, cows didn’t favor one water treatment over the other in the 0-to-4 ppm range. But their water consumption went down 25 percent when there was 8 ppm of Fe in the water.

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In the second experiment, with 0 or 8 ppm Fe from either ferrous sulfate (FeSO4) or ferric sulfate [Fe2(SO4)3], and in a third experiment with 12.5 ppm Fe from ferrous chloride or 8 ppm Fe from ferric chloride, water consumption tended lower compared with 0 ppm but was not statistically significant.

Also, water intake tended to decline more with ferrous Fe+2 from either the sulfate or chloride sources compared with the ferric Fe+3 sources. In the final experiment, testing treatments of 0 or 8 ppm Fe from among ferrous lactate, ferrous sulfate or ferrous chloride, water intake by cows was about 34 percent less with added iron compared to 0 ppm, but intake of water among added ferrous Fe+2 treatments did not differ.

“We were a bit surprised in the first experiment that drinking water preference and consumption were not reduced except by the 8 ppm iron treatment (from ferrous lactate),” Beede says. “We thought 4 ppm also might affect water intake too, but it did not.

Also, note that we did not test preference or water intake for iron concentrations of, for example, 5, 6 or 7 ppm iron, so we do not know if these concentrations might also affect preference or reduce water intake.”

So based on the research to date, a question remains for dairy producers: How do you achieve acceptable levels of iron in drinking water with the appropriate valence?

First, according to Beede, iron concentration needs to be determined by laboratory analysis of drinking water samples. If iron concentrations are in excess of recommendations, then follow-up action can be taken with more comprehensive troubleshooting of the herd.

“If the concentration is greater than 2 ppm Fe, then additional evaluation and diagnostic work should be done in the herd to try to ascertain if the drinking water might be an issue. For example, are there fresh- cow problems, or metritis or mastitis that the producer would evaluate as normal?

In practical conditions, the valence of iron probably is not an important factor; we presume that most of the iron is the ferrous Fe+2 valence, soluble in water and thus potentially very absorbable by the cow.

So, if it is determined that the concentration of total recoverable iron in the water is a potential problem, then it might be indicated to treat the water to convert the ferrous iron to ferric iron by an oxidation process using hydrogen peroxide, chlorination or simple aeration and then filter out the ferric Fe+3 iron that is formed,” he explains.

“The only way to know for sure if drinking water in a particular dairy farm has excess concentrations of iron or anions (such as sulfate and chloride of more than 250 to 500 ppm) is to have water samples analyzed periodically by a reputable laboratory,” Beede adds. Procedures for sampling are listed on his university website page – click on Extension and then “Taking a Water Sample.”

Beede says the results also support the need for laboratories, when analyzing iron in drinking water for dairy cattle, to acidify the water samples in preparation for analysis, before the actual analysis to detect the iron.

“Acidifying the sample before analysis solubilizes all of the Fe in the sample and results in complete quantification of total recoverable iron.

Not acidifying will result in detection of only a part of the total iron in the sample – in our experience, only about one-fourth of the total recoverable iron is detected if the sample is not acidified.

Thus, without acidification, a false low reading of the total iron in the water sample would result, not providing a true picture of total iron in the sample,” he says.

According to Beede, water treatment methods are available to remove iron (oxidation by hydrogen peroxide or chlorination, each followed by filtration).

Hydrogen peroxide treatment may be preferred because its half-life in water is relatively short, whereas aggressive chlorination can result in residual chlorine in the drinking water that can affect the cow’s rumen micro-organisms and reducing milkfat test.

For excess sulfate and chloride in drinking water, reverse osmosis is the treatment of choice; however, cost is a major issue.

If water quality problems are detected, it may be most feasible long term to locate another water source, such as drilling a new well or finding another alternate source of drinking water.

That may be the most cost-effective management decision compared with extra cost, labor and long-term maintenance of a water treatment system.

“The number one priority should be to routinely test drinking water quality twice per year, with one test being in the late summer when water levels in groundwater wells are likely to be lowest and concentrations Fe, sulfate or chloride could be highest,” Beede says.

“If laboratory analysis indicates concentrations of various analytes above suggested upper threshold levels, then additional analysis of water intake, feed intake, herd health and cow performance would be indicated to determine if a new drinking water source, or water treatment system might be worthwhile.” PD

Stephanie Skernivitz is a freelance writer based in Berea, Ohio.

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