What is the REAL resistance of a Dairy Cow?

Cow Resistance - Critical to determining whether stray voltage exists on your farm is determining the current that can access the cow. It is important to remember that it is current, not voltage, that causes harm to animals. Testing for current involves application of Ohm’s Law. V = I X R, where v = volts, I = current and r = resistance. For any given voltage, current will be higher with lower resistance. This means, when testing for stray voltage, it is important to use the correct resistor to represent the cow in the circuit. For decades, utility companies have been testing for stray voltage on farms with equipment that uses a 500ohm resistor to represent the cow plus cow contact. Research shows this level of resistance grossly overstates the true resistance levels under most pathways. This is especially true for the most widely accepted "Nose to 4 Hooves" pathway (representing a cow eating or drinking). Using a 500-ohm resistor in the test circuit will report lower current and allow the utility to tell the farmer that stray voltage does not reach the “level of concern” (the level of either current or voltage that requires corrective action by the utility). The links in this section will take you to the historic and current academic research and real-life field data as well as expert testimony given under oath, that supports a much lower lever of resistance should be used.

Why is it important to establish and test with a resistor that accurately depicts the worst-case scenario on a farm? Simply stated, every cow has a different resistance to current and every cow matters. If even 10% of a herd is affected, it can be devastating to the herd's well-being and the bottom line. Most utility companies will not work to identify or correct a problem unless they find 0.5 - 1.0 volt or 1 mA - 2 mA at cow contact points. By using a resistor of 500 ohms, the utilities under-report voltage and current accessing and going through the animal. This means that farmers aren't able to meet the "level of concern" when in reality they do. Until this level of concern is met, the utility companies claim no obligation to help find or remedy the problem.

500 ohms? Why?

Many hours have been spent trying to unsuccessfully explain why 500 ohms was selected by some of the authors of the "Red Book" as the resistance of the pathway for current through a cow. Let's go through it step by step and you will plainly see that 500 ohms SHOULD NOT be the standard used in the industry for testing for stray voltage.

First, the pathway for current that goes through a cow to complete a circuit is from a source, goes along a pathway to a contact point, and from a cow contact point (for example, 4 hooves contacting concrete in a free-stall barn) to the cow itself, a second contact point (nose/mouth with a waterer) from the cow to the pathway back to source. When you add all of those resistances together, you get a total number. The authors of the Red Book agreed with the science that said the source and pathway resistance can be assumed to be zero (See page 7-6 of the Red Book shown below). So that leaves the resistance number used in the equation (V = I x R) and in farm testing to be the combination of the cow and the cow contact resistances. The authors of this chapter of the Red Book, claim that 500 ohms is the "worst case circuit impedance*" for cow plus contact measurements.

It is clear in all of the research cited in the Red Book and all research done since the publishing of the Red Book, 500 ohms is **not** the worst-case circuit impedance of a dairy cow. See table 7-1 below, which lists all the research available at the time of the white paper's publication. There is also a list of additional research done after its publication and testing results from hundreds of cows done on individual farms that also does not support 500 ohms as being the worst-case scenario.

So how did the authors come up with 500 ohms to be the lowest resistance that should represent the "worst case" scenario? That's a great question that has yet to be answered. The research confirms that cow resistance/impedance without contact resistance is commonly in the range of 150-250 ohms taking the pathway of nose/mouth to all four feet. Using 500 ohms would mean you would have to add 250 to 350 ohms for contact resistance. However, that doesn't square with science. Dr. Robert Gustafson, one of the authors of the Red Book, testified that contact resistance of a hoof on wet concrete and a nose on a wet surface will be 1-5 Ohms. So according to one of the two electrical/Ag engineers that were authors of the Red Book, the cow contact impedance will only add 5 ohms to the cow's resistance. That is a far cry from 250-350 ohms needed to get the cow plus cow contact to 500 ohms.

Below, you will find a deposition done with Dr. Gustafson, where he verifies on page 69 that the cow contact resistance is 1-5 ohms for a cow standing in manure/urine/ water mixture, like would be found around a waterer in a barn. There is also a sworn deposition of Dr. Aneshansley, who is another author/electrical engineer of the Red Book. He verifies under oath that he would trust the conclusions made by Dr. Gustafson in regard to his work on cow contact resistance being between 1-5 ohms. That is found on page 80 of his deposition. Dr. Aneshansley also testifies that since the papers cited in the Red Book show the lowest cow resistances below 244 ohms and the cow contact resistances well below 200 ohms, that then the worst-case scenario for resistance should NOT be 500 ohms. This is on page 89 of his deposition. Dr. Gustafson, on page 67 of his deposition, acknowledged his own research showed resistance of a dairy cow to range 250-350 ohms. His research was done many years ago in a very different cow environment then what is found on modern farms.

The Red Book quickly became the handbook referenced around the world by utilities when conducting testing. Legislative hearings, state testing procedures and even course studies were developed using the much overstated 500 ohms resistance when testing dairy farms for stray voltage. Even 30 years after its publication, it continues to be used in testing despite there being NO SCIENTIFIC EVIDENCE to back that number - EVER.

To sum this discussion up, Drs. Aneshansley and Gustafson are both engineer/scientists who have worked extensively in litigation cases on behalf of utility companies. Both have acknowledged facts in sworn depositions that proves 500-ohms does not represent the worst-case circuit impedance for cow plus cow contact. So how low is the worst-case scenario for cow resistance? Scientific research done in 2020 with randomly selected cows shows minimum body resistances of 141-ohms as found in Dr. Richard Norell's abstract found above. Since every cow in every environment has not been tested in a scientific study, the full range, and therefore lowest cow measured, is still unknown at this point. Thankfully, we have field investigations which give us additional data to pull from. The data shown in the table below, with testing conducted by Concept Electric, shows the lowest cow tested at 109-ohms. Therefore, based on both peer-reviewed and scientifically conducted field studies, the worst-case scenario for cow plus contact resistance should be the combination of the lowest tested cow plus cow contact (5-ohms). **NOT 500 ohms**. Many of the top Ag organizations are promoting the use of a 125-ohm resistor for stray voltage testing on farms.

*The Red Book uses resistance and impedance interchangeably. There is a technical difference between them, however, the Red Book largely ignores the difference for this purpose.

It was USDA Publication 696: Effects of Electrical Voltage/Current on Farm Animals. In the preface of this handbook, it states that the publication is a "White Paper" and that it was put together out of concern, in part, for their research being used in lawsuits.

According to Wikipedia, the definition of a

**white paper** is "A report or guide that informs readers concisely about a complex issue and presents the issuing body's philosophy on the matter. It is meant to help readers understand an issue, solve a problem, or make a decision. The term originated roughly a century ago to mean a type of position paper or industry report published by some department of the UK government.

In more recent years, this type of document has proliferated in business. *Today, a **B2B** white paper is closer to a marketing presentation, a form of content meant to persuade customers and partners and promote a certain product or viewpoint."*

The Red Book is NOT a peer reviewed document and Dr. Anashesley has testified that some of the authors DID NOT agree with the conclusions in it. See page 198 of his sworn deposition.

To our knowledge, at least six of the contributors to the Red Book have testified on behalf of utility companies.

This single page of the Electrical handbook, commonly referred to as the "Red Book" for its original color, highlights the problems surrounding the procedures used while testing for stray voltage. **Table 7-1** **Resistances of various electrical pathways through the cow**, is a list of research conducted prior to the publishing of this handbook in 1991. Some of the studies looked at various pathways that electrical current could take in a typical dairy operation. Mouth to all hooves is the pathway of greatest concern since it is the pathway that represents a cow eating or drinking, something a cow cannot avoid while maintaining life. The research shows that the measured resistance of the cow plus cow contact ranged from 244 - 525 ohms and 324 - 393 ohms in the 2 studies that measured mouth to 4 hooves. Also note, the footnote under the table. It states that in the Norrel et al, 1983 study that the posted range only represents the 10th-90th percentile of cows. This means 10% of the cows in the study had a resistance below 244 ohms.

Yet, in the paragraph just below the table of published research, the author of this page chose to disregard the studies listed and state that a realistic resistance of a cow plus cow contact is 1000 ohms and the "worst case impedance" (resistance) is 500 ohms. This clearly does not represent the science for mouth to all hooves pathway. And nearly all the other pathways listed show the lower range of resistance to be well below 500 ohms. Yet, 500 ohms is the resistance that is used by the utility industry to conduct its testing.

Why is using the correct resistance level so important? Its all about the science. Check out the page that explains v = i x r and how a wrong assumption of one factor will affect the other factors in the equation.

Reviews of Resistance Testing Literature

Following are reviews of literature done by Aaron Rendahl Ph.D, and the late Frank Martin Ph.D. They reviewed the data, statistical calculations and conclusions of research relied upon for stray voltage mitigation. These reviews contain not only reviews on the resistance levels, but also studies that talk about the effect stray voltage has on a herd. They will be referenced in other areas of this website.

Real Farm Field Data

The following table shows results from on-farm resistance testing for herds across the US. The testing was done on the pathway of nose to all four feet - as this is the pathway of the greatest concern as it depicts the contact points of a cow which is eating or drinking. Over 800 cows were tested, mostly Holstein, but also some Jerseys and Brown Swiss. The range of resistance for the cows plus cow contact was 109-395. Every animal tested is well below the 500 ohms that is being used in testing protocols published by utility groups. The average is 215 ohms which is less than half of the suggested 500 ohms worst case scenario.

Photo Gallery

Photo of the resistance testing set-up showing the grate the cow will stand on that ensures she is completely separated from the gound. This setup is used when measuring nose to four hooves.

Notice in most on-farm testing, cows are tested on dry clean surfaces. In the real world, one would expect to find varying amounts of wet manure and liquid that the cow would stand on, further reducing resistan

This photo shows the cow is isolated from the chute she is held in so only the cow's resistance is being tested. Also note, in this case, a "nose lead" is being used to take the measurements. In some scientific studies a metal bit or basket were used, with identical results on the cow contact. Since a nose lead is less invasive and in no way hurts the cow, this is the preferred method for on farm

On farm testing uses Ohm's Law, V = I x R. When you know two of the factors, you can calculate for the third. When testing cows for resistance, the voltage and current are the known factors and the resistance can then be calculated.

Copyright © 2024 Stray Voltage Awareness - All Rights Reserved.

Powered by GoDaddy

We use cookies to analyze website traffic and optimize your website experience. By accepting our use of cookies, your data will be aggregated with all other user data.