A REVIEW OF STRAY VOLTAGE RESEARCH:
Effects on Livestock
Robert J. Fick, Ph.D.
Agricultural Engineering Department
Michigan State University
East Lansing, Michigan
Truman C. Surbrook, Ph.D., P.E. Professor
Agricultural Engineering Department
Michigan State University
East Lansing,
Michigan Topics included:
A Review of Stray Voltage Research: Effects on Livestock
- Introduction
- Stray Voltage Definition
- Types of Electrical Exposure
- Evaluation of Results
Summary of Research
- Currents
- Voltages
Research Conclusions
The Michigan Agricultural Electric Council (MAEC) has completed this review in the interest of informing the electric power, agricultural and university communities about the results of the total body of research on the effects of stray voltage on livestock. Stray voltage was not widely recognized as a phenomenon in the United States until the early 1980's and the majority of the research on stray voltage has been performed since that time.
In 1991, a group of agricultural scientist published the USDA Agricultural Handbook, 696, Effects of Electrical Voltage/Current on Farm Animals: How to Detect and Remedy Problems (USDA, 1991). The purpose of the USDA handbook was: a) to prevent research results from being misinterpreted and misconstrued, and b) to improve the understanding of causes and effects of stray voltage on farms.
For this review, all available research on the effects of stray voltage on animals, including that completed since 1991, was collected and reviewed. This document provides summaries of the studies where variables other than the treatment were controlled (repeatable research), and presents the results to address the following:
- Provide a summary of conclusions of research findings.
- Explain how the different research trials were conducted.
- Explain the different methods used by researchers to determine if animals were being affected.
Stray Voltage Definition
Electrical systems on farms and electrical supply systems delivering power to farms, homes, and businesses are grounded to the earth to help assure safety and reliability. The grounding of these electrical systems results in some current flow through the earth. Associated with this current is a small voltage which develops at each point where the electrical system is grounded. That voltage is called neutral-to-earth voltage (NEV). When the NEV is found at animal contact points, it is frequently referred to as stray voltage.
Stray voltage is this small voltage (usually less than 10 volts) that is measured between two points a livestock animal can simultaneously touch. If these points are simultaneous contacted by a livestock animal, a current will flow. The amount of current depends on the voltage and the circuit impedance (For most situations, impedance and resistance are equal in animal circuits), which includes the source, contact, and body impedances. Livestock respond to the resulting current flow and not the applied voltage.
Types of Electrical Exposure
Most exposure an animal may have to electricity in its environment is alternating current (ac) with a frequency of 60 cycles per second (Hertz or Hz). The 60 Hz ac flows first in one direction and then in the other, 60 times each second. The majority of the stray voltage research has been conducted at 60 Hz.
Direct Current (dc) on the other hand flows only in one direction. A chemical battery, a found in a tractor or car, typically produces dc. Different metals making contact with damp earth sometimes will act as a weak battery producing a voltage between two points.
An animal may also be exposed to an ac frequency that is higher than 60 Hz. Some of the research was conducted with the ac frequency as high as 50,000 Hz. Frequencies of ac less than 60 Hz are not known to be observed in the animal environment.
Animals may also be exposed to current that lasts for only a fraction of a second. Currents that last less than 1/2 of a 60 Hz cycle (about 1/100 of a second), are usually called transient currents. Some research was conducted to test for effects on animals with transient currents. The operations of contractors or switches are examples of transient sources. The currents from fencers are regular intermittent dc transients.
Currents that are greater than 1/100 of a second in duration but are less than one or two seconds are sometimes called momentary currents. The in rush current during an on-farm motor start is a common source of a momentary current.
An animal can be exposed to many different types of electrical current and voltage in its environment. Researchers used varying techniques and tried to duplicate any exposure an animal could receive. They also used differing methods to determine animal effects. Therefore, careful considerations should be given to the specific variables when comparing individual research trials. This document tries to categorize the different research trials to help the reader understand how an animal may be affected in an actual farm situation.
The threshold level for an animal's perception and response to an electrical current is widely variable between animals. The threshold for even one animal can change over time. Research was concerned with the determination of the lower threshold for a livestock population.
The pathway for current through an animal with the least resistance is from the mouth to all hooves. Due to this pathway being the most sensitive for the animal, much of the research has focused on current or voltages at feeders and waterers. This is especially true for long term studies.
Evaluation of Results
This evaluation of research results was started by grouping the findings of research trials as perception, behavior changes, and production losses (Table 1). Perception involves an animal's initial awareness of current. Animals cannot tell us when they first perceive current, therefore, researchers can only look for initial changes in normal behavior. Indications of perception that have been used by researchers include: the lifting of a leg, training animals to perform a specific task in response to stimulus, flinches, shifting of weight, blinking of eyes and other minor observable actions.
Behavior change will normally involve some type of avoidance by the animal. When exposed to the electrical current, an animal may position or move itself so that it is no longer a part of the electrical circuit. Behavior change may be identified when the animal: avoids an object or area, changes its manner of drinking, flinches or exhibits other behavioral modification. All of these changes can also be associated with normal behavior, making the interpretation of behavior difficult at times.
A production loss occurs if water or feed consumption is reduced for a sustained period of time. In some trials, it was noted that an animal acclimated after a period of time to the presence of a current or voltage between animal contact points by resuming normal water and feed consumption patterns. This was not considered a production loss if weight gain or milk production was not affected.
Summary of Research
Voltage (All values of current and voltage are root mean square (rms) unless otherwise noted) is required between animal contact points before current can flow through an animal, but current must flow through the animal before it can be affected. The electrical quantity that an animal or a person feels or reacts to is electrical current. The levels of electrical current that can be perceived by an animal or a person is in the range of a few milliamperes (mA). One milliampere is 1/1000 of an ampere (A). An electrical pressure or voltage is required for electrical current to flow through the body of an animal or a person. If an animal simultaneously makes contact with two conducting points with a voltage between them, a current can flow through the animal's body. Electrical current must flow through an animal before the animal can be affected.
The relationship between voltage (V), current (C) and resistance (R) is described using Ohm's Law: V = C x R. Current flow through an animal's body is equal to the voltage between body points divided by the animal circuit resistance: C = V / R.
Voltage is normally measured between two points that an animal can simultaneously contact. By estimating the total circuit resistance, which includes the resistance of the animal, the amount of current that could flow through an animal's body can be determined using Ohm's Law. This research review presents the results in current except in cases where only voltage between animal contact points was measured.
Currents
Animals may perceive currents through the body below 3.0 milliamperes (mA) at 60 Hz without any resulting behavior problems. Under unusual circumstances, an animal may be able to perceive currents below 1.0 mA. The perception level for an animal will vary greatly depending on the animal circuit pathway and points of application. Lefcourt (1982a) found that pigs could detect a difference between a water nipple with no voltage present and one where the pigs were exposed to 0.25 mA.
Behavior changes that were found by researchers in the 3.0 to 6.0 mA range (60 Hz) caused only short term effects and did not affect overall production. Management or handling concerns may occur when an animal's body current exceeds 4 mA.
None of the research showed changes in production or feed or water consumption for currents at or below the 4 mA level. Lefcourt (1982a) measured a production decrease in one study at 5.0 mA, but a subsequent study measured no decrease in milk production at 6.0 mA. Currents of 5 mA and 6 mA had no effects on long term production in any other study.
As frequency is increased above 60 Hz, the response threshold rises (Reinemann et al., 1995a and Aneshansley et al., 1995). The average threshold for an animal response when exposed to a 0.017 second pulse every two seconds for thirty seconds was 5 mA at 60 Hz, 26 mA at 6000 Hz, and 132 mA at 50,000 Hz (Reinemann et al., 1994).
Based on the research conducted, it is improbable that currents can be sustained through an animal during milking at a level that will decrease milk production, without behavioral problems first becoming prevalent.
Physiological effects on animals can be determined by observing changes in hormone levels due to an electrical stimulus. No hormone level changes were observed at 5 mA or below. Changes in cortisol levels were observed by Henke-Drenkard et al. (1985) and Aneshansley et al. (1992) at 8 mA.
Limited research has been done with direct current (dc). Based ontwo sets of experiments for perception and behavior by Gustafson et al.(1985 and 1988), the threshold values for dc are 20 to 30 percent higherthan those for ac.
Voltages
Current flow measurement through an animal's body on an actual farm is not practical. As a result, research was conducted where a specific open circuit voltage was applied across animal contact points. Current flow through any particular animal will vary as a function of the animal circuit resistance. The resistance of an animal's body is only part of the total circuit resistance that includes the animal.
No water or feed consumption reduction was observed for any livestock below a threshold of 4 volts (V) applied continuously between animal contact points (60 Hz). However, two out of 30 animals in one test by Gorewit et al. (1989) refused to drick at 4 V for 36 hours and were given alternate water source. No other research found any statistical effect on overall consumption or production at 4 V and below.
Voltage applied randomly between contact points has less effect than voltage of the same level applied continuously. No losses in water or feed consumption or production were found by Godcharles et al. (1993) where pigs were exposed to a continuous baseline level of 5 V with intermittently applied three-second pulses up to 8 V between feeders or waterers and a metallic floor. Aneshansley et al. (1988) applied one-second pulses of 8 V both randomly and intermittently at waterers for twenty-one days with no effect on feed or water consumption or milk production.
Reproductive parameters including days to first estrus, conception rates, calving interval and number of calves born dead were evaluated in full lactation studies by Gorewit et al. (1990) and Gumprich (1994). No change in any breeding parameter was found for any treatment, (the highest treatment levels were 4 V and 5 V respectively). Twelve and 13 week studies of voltage effects on fattening pigs by Robert et al. (1992) and Godcharles et al. (1993) examined blood samples every two weeks and meat and stomach conditions after slaughter. No statistically significant change in blood or tissue samples occurred for voltage treatments (highest treatment was 8 V).
Research Conclusions
Review of all research publications on effects of electrical current on animals indicates that the findings of USDA Agricultural Handbook, 696 Effects of Electrical Voltage/Current on Farm Animals were accurate. Figure 3-4 from USDA 696 (included as Figure 1) is a realistic representation of the responses of animals to currents. The Diagonal line in Figure 1 (on the following page) represents the biological variability that exist in animals.
To eliminate the possibility of production loss, the amount of current that can flow through a body of an animal should be kept below 4 mA (60 Hz). None of the research showed a decrease in feed or water consumption or milk production at a level of current through the animal below 4 mA (60 Hz).
No overall decreases in feed and water consumption or milk production will occur below 4 V. A practical value for animal circuit resistance is 1000 ohms based upon research that shows no feed, water, or production loss below 4 V across an animal body or a body current of 4 mA (4 V / 4 mA = 1000 ohms).
Voltage should be monitored as an indicator of potential stray voltage problems. It is not appropriate to monitor only animal behavior because there are many other animal environment factors beside stray voltage that could cause these changes.
While no research has found production losses for 60 Hz animal body currents below 4 mA or for voltage between animal contact points below 4 V, a conservative practice of keeping animal currents at or below 2 mA and voltages between animal contact points at or below 2 V will provide a margin that will prevent stray voltage from causing a problem.
The tables for A Review of Stray Voltage Research: Effects on Livestock are not available on the web. A complete copy of this document including tables can be obtained through MSU Extension services:
MSU Bulletin Office
10-B Agricultural Hall
Michigan State University
East Lansing, MI 48824-1039
Telephone: (517) 355-0240
Fax: (517) 353-7168In Reference to New 6:96-2M-KMF, File 18.34 (Electrical Wiring), Extension Bulletin E-2606.
The repeatable research studies dealing with effects of electrical current on livestock were reviewed and presented in tables to facilitate comparison. The tables were didvided into Experimental Discriptions, Treatment or Test Levels, and Results. The Results are categorized according to threshold values for 1)perception, 2)behavioral response, and 3)production loss. The papers and articles reviewed are listed in the bibliography.
More information about A Review of Stray Voltage Research: Effects on Livestock
Truman
Surbrook, Ph.D., P.E., Professor & Managing Director
Department of Biosystems & Agricultural Engineering
Michigan State University
103C Farrall Hall
East Lansing, MI 48824-1323
Office: (517) 353-3232
FAX: (517) 432-2892
Email: surbrook@egr.msu.edu
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November 13, 2007
