Current Progressive Dairy digital edition

Stray voltage affects cow behavior, milk production

Progressive Dairyman Editor Emily Caldwell Published on 06 January 2015

water trough

Editor's note: The following information was presented in a Sept. 23, 2014, webinar by Dr. Douglas Reinemann of the University of Wisconsin – Madison. The webinar is part of Penn State Extension's Technology Tuesday series and is available at the Penn State Extension website.



A common myth is that stray voltage can cause mastitis. But in more than 20 years of stray voltage advising and research, University of Wisconsin – Madison's Dr. Doug Reinemann has found that's not the case.

"When you look at the literature, there have been 20 or 30 different studies where cows were exposed to different voltage levels and for different durations," he says. "There are no studies that support the hypothesis that stray voltage exposure up to 8 volts will result in increased somatic cell counts or incidences of mastitis."

Determining problematic levels of stray voltage

Research trying to determine thresholds of behavioral responses to stray voltage shows that:

  • 2.5 milliamps of current will impact the 5 percent most sensitive cows of a herd.
  • 4.8 milliamps will cause an effect for the 50th percentile.
  • 8.5 milliamps will cause 95 percent of cows to adapt their behavior.

This threshold is a mild behavioral response – something as subtle as a flicking of the ear or twitching of the nose. Current levels required to cause an adverse response, such as avoiding drinking, are two to three times higher than these thresholds.

Wisconsin and many other states have an on-farm limit of 2 milliamps or 1 volt cow contact locations. Most cows will not have an aversion to current until levels of 8-16 milliamps, with the most sensitive cows having no aversion until 4-5 milliamp exposure.


Common animal responses often attributed to stray voltage and corresponding researched voltage levels include:

  • Milk production – Some effect was shown at exposure levels of more than 8 volts. The exposure was extreme, meaning that exposure was unavoidable, such as at a watering trough.
  • Somatic cell counts – No effect has been documented of exposure levels up to 8 volts.
  • Reproduction efficiency – No effect has been documented of exposure levels up to 8 volts.
  • Milkout problems – Some effects have been documented of exposure levels up to 12 volts.
  • Stress hormones – Some effects have been documented of exposure levels up to 16 volts.

"The question is, 'Can stray voltage affect cows?'" Reinemann says, "The answer is ‘Yes,’ but what we need to determine is, 'At what exposure level will it be problematic?'"

Reinemann and his team found that if the voltage is problematic at a water bowl, cows will drink less often but drink more water. They drink as much as they can as fast as they can by deeply submerging their muzzle to reduce the sensation of voltage.

When diagnosing your farm for stray voltage, it's important to recognize that cows must be exposed to the voltage for it to have an effect.

"Even if I have areas of the farm with 4 volts, if that voltage is in areas not vital to normal daily activities of the cows, it's not going to impact them," Reinemann says.

Further, a voltage spike that occurs on a waterer only once per day is unlikely to alter the cows' behavior.


Reinemann says many producers express concern about stray voltage in the parlor, but in fact, the parlor is one of the most unlikely locations for stray voltage problems. This is because milking machines, hoses and liners have very high resistance. It would take an enormous amount of voltage to drive current through a milking unit. In addition, parlors are usually well bonded. So the milking stalls, equipment and flooring produce an equipotential plane that reduces stray voltage.

Problems can occur, Reinemann says, but it's much less likely in a parlor than in other areas on the farm.

Diagnosing stray voltage

"If you want to know whether or not electricity is causing harm to your cows, you need to have a good electrical measurement performed," Reinemann says. "The only thing that will be able to tell you whether or not electricity is problematic is a competent stray voltage investigation that measures the cow contact voltage potential in the cow environment on your farm. In order to do a proper investigation, it does take a certain amount of skill and the proper equipment."

If you can't measure the cow contact voltage, the problem likely isn't stray voltage, he says. If it's there, you should be able to measure it and reduce it. If the voltage isn't high enough to cause the issues you’re seeing, you've either taken the measurement incorrectly or the problem is being caused by something else. When it comes to behavioral modifications, mastitis issues and milk production decreases, many other factors could be the culprit.

Avoiding ineffective solutions

Reinemann has seen a "steady stream of unorthodox approaches" in his years of stray voltage research. Each year, he says, it seems there's a new "cure-all" device on the market that promises to solve stray voltage problems. He urges producers to carefully review these devices and ask themselves, “Is it safe?,” “Is it technically effective?” and “Will it actually help the cows?”

The vast majority of problems can be solved by applying accepted electric codes, he says. If you wire your farm according to the National Electric Code, it's the best protection against a stray voltage problem. When there is a problem, it's often because the electrical system wasn't installed properly in the first place, the system has been damaged or corroded, or the system no longer conforms to the code. Most of the problems he has seen are a result of a bad connection on a neutral wire. Once that connection has been found, it's generally easy to fix.

When hiring a stray voltage investigator, Reinemann recommends that producers ask where the individual has received training. University of Wisconsin – Madison, Cornell and Michigan State have all run courses related to stray voltage testing. Producers may find it beneficial to enroll in one of these programs themselves. PD

Visit the “Agricultural Wiring & Stray Voltage” section of the Midwest Rural Energy Council website for more information about this topic.

Photo by Progressive Dairyman staff.