Dairy Cattle - Stray Voltage Problems in Livestock Production
Stray, tingle or neutral to earth voltage has been implicated as a problem for dairy and other livestock herds for approximately twenty years. For the livestock producer, awareness of and concern for tingle voltage should be one small component of the overall concern for the management and profitability of the herd, and the well being and productivity of the animals. Recent research has focused on measuring the tolerance for and economic impact of exposure to low levels of tingle voltage. These studies suggest that under most normal farm conditions, stray voltage is of less concern than suggested by literature published in the previous decade. Earlier studies focused on defining the "sensitivity" of livestock, resulted in recommendations for corrective action at very low levels. A further understanding of tolerance levels resulting from more recent trials indicate there is little cause for concern in the 0.5-2.0 volt range commonly found between surfaces contacted by livestock. Higher levels may be detrimental in wet environments and should be resolved in a low cost and effective manner.
By its nature, livestock production involves numerous variables including nutrition, genetics, infectious disease and environmental factors including stray voltage. As a relatively small element in this complex production system, stray voltage is at least as well researched and understood as other components. At the farm level, however, it remains poorly understood largely because it is isolated technology not central to the training and focus of agribusiness or extension. When unexplained production problems occur on livestock farms, emotion and misinformation often lead to assignment of responsibility to the most poorly understood potential causes, preferably those which are perceived as outside of the control and responsibility of the manager. Today, stray voltage is thoroughly researched and can no longer serve as a "scapegoat" for the unexplained.
Small electrical potentials or voltages between metal stabling and equipment, and floor surfaces are natural, explainable and expected phenomena in livestock facilities, served by grounded neutral electrical systems. The voltage originates on the current carrying neutral conductors of the electrical system. Ohms Law (voltage = current x resistance) predicts that all passage of electrical current is associated with voltage proportional to the resistance and amount of current involved. Metal stabling, water lines and case grounds on electrical equipment are all bonded back to the neutral of the system at the service entrance panel, primarily for safety reasons. As a result of these bonds, all of the stabling, etc., becomes an integral part of the return path of electrical current to the transformer it originates from. Livestock which come in contract with stabling, bowls, etc., can receive a shock as they become part of this complex configuration of electrical pathways for current flow. The current on barn neutrals has the following origins:
Currents from each of these sources can have differing phase relationships to each other and either cancel or compliment the other sources. A simple test to determine which sources make a major contribution to the tingle voltage present on a dairy farm is included as Appendix 1, taken from the University of Minnesota Publication, "Stray Voltage Problems with Dairy Cows". While this procedure is appropriate for "troubleshooting" a problem situation, it is highly recommended that only readings taken between animal contact surfaces be used to establish to presence of "problem" levels of stray voltage. Research has shown a wide variation in the relationship of voltages measured between the service entrance neutral and remote earth vs. those between animal contact surfaces.
A survey of 140 Ontario dairy farms showed that 80%, 55% and 28% of herds had peak voltages between the service entrance neutral and remote earth in excess of 1.0, 2.0, and 3.0 volts respectively in a 24 hour period. Highest voltages were usually recorded during peak electrical load periods between 6 and 9 a.m. and 5 and 8 p.m. On measurements taken between cow contact surfaces, 50%, 21% and 11% of farms exceeded 0.5, 1.0 and 2.0 volt peaks respectively. On 40% of the farms, cow contact voltages were very low in spite of the presence of voltage on the neutral, because there was no low resistance bond to stabling, even though this is required by the electrical code. In this study, nearly all of the voltage found could be attributed to primary neutral resistance in the distribution system. Only a few isolated cases were identified in which on-farm faults or wiring problems made a major contribution. On-farm electrical faults, when they were identified, did typically involve higher voltage readings.
The reactions of animals to mild electric shocks caused by stray voltage have been reported to include behavioural changes, changes in milking characteristics of dairy cows and changes in production performance. Both research and on-farm observation have documented the following behavioural changes in dairy cows:
These three symptoms may occur as a result of tingle voltage, or may be caused by a number of other factors including rough handling of cows in the parlor, malfunctioning milking equipment or changes in the parlor environment, such as the presence of strangers. Although similar symptoms may occur in tie stall housing at milking time, the wet, bedding free, short time exposure situation created by parlor milking appears to be associated with a stronger expression of symptoms. Although only about 20% of Ontario herds are milked in parlors, more than half of the stray voltage problems I have been involved with, involved milking parlors. The above three symptoms are probably the strongest evidence of stray voltage in the dairy herds.
Reduced feed intake or water consumption has been a well documented symptom of stray voltage in beef and dairy cattle, as well as swine and poultry. Changes in drinking behaviour such as lapping at water bowls and longer, less frequent drinking usually occur at lower levels of voltage than a decrease in water intake. Cases of refusal to use computerized feeding stations or specific water sources have been clearly associated with stray voltage in field studies. Unlike parlor behaviour patterns, dairy cows have shown considerable ability to adapt to stray voltage on water bowls. In research trials, cows that totally refused water from electrified bowls for up to 24 hours at first exposure, consumed normal amounts of water after the first day. Results with swine are similar and discussed in more detail later in this paper.
The above symptoms should be considered "primary" in that they have been specifically linked directly to stray voltage. While they may result from other causes, their presence is good justification for stray voltage investigation. Secondary symptoms listed below should be considered potential results of the behavioural symptoms listed above. When these secondary symptoms are present without the nervousness, etc., described above, their cause is likely to be unrelated to stray voltage. Reported secondary effects of stray voltage include:
In summary, stray voltage problems alter animal behaviour and may influence milking characteristics and/or affect production performance. If unacceptable levels of stray voltage are known to exist, corrective action should be taken. It must be remembered there are many other non-electrical causes of the same symptoms. With careful analysis of all possible causes, proper corrective procedures can be found.
Attempts have been made to associate the problems of unthrifty and unhealthy animals, poor reproduction and weak calves with stray voltage. The failure of controlled research to find a direct physiological effect in animals subjected to stray voltages, and the absence of documented case studies demonstrating a marked improvement in these traits upon correction of an existing problem, leads to the conclusion there is no direct and causal relationship.
Numerous studies have been conducted to try to establish to level of stray voltage which warrants corrective action, however, to date, no single clear answer has emerged.
Animal response depends on the magnitude of the "shock" it receives which is a function of the amount of current flow, and on the sensitivity to shock of the animal itself. The measured voltage between cow contact points is only one component in determining the current flow which will occur on exposure. The electrical resistance at contact points and within the animals body is equally important and highly variable. Cows with poor hooves, wet environment and lack of bedding may be more subject to shocks at lower voltages due to decreased contact and internal resistance. The type of contact with stabling may also be a factor. For example, the pathway for current flow through a neck chain tied to stabling has a much higher resistance than through a water bowl to the cows nose. Specific studies examining the possibility of cows receiving a shock from the milk claw, show that with 9 kg per minute milk flow in a plastic long milk hose, the resistance to a high and low line pipeline is 47 Kohm and 26 Kohm respectively. With this extremely high resistance, the voltage measured from the pipeline to the cow platform would have to be 47 and 26 volts respectively for cows to get a 1.0 milliamp shock through this pathway. In view of these studies, it is clear that cows do not get shocks directly from milking systems through the claw. Studies with current delivered from the mouth to hooves of dairy cattle in an environment which minimized contact resistance, indicated an avoidance reaction with currents of 1.0 to 4.0 ma AC. The same workers measured electrical resistance of dairy cows and determined an average value 390 ohms. Based on this work, it would appear that dairy cattle can "sense" currents of 1.0 to 6.0 ma AC and demonstrate a mild avoidance reaction at these levels. Using a 390 ohms resistance value, this translates to a threshold sensitivity of 0.4 to 2.4 volts. These studies were the basis for the previously accepted, low threshold used to define potential problem situations. Studies which attempt to assess impact of stray voltage on economically important behaviour such as feed and water consumption, milk production, health and reproduction, show tolerance to be much higher than this.
In two studies measuring drinking behaviour in cows exposed to from 0 to 4 volts on water bowls, all levels of voltage caused a delay in the initial time to consume the first gallon of water from 2 to 36 hours depending on voltage level. In total, 7 out of 110 animals refused to drink from bowls electrified with 5-6 volts and these animals were removed from the trials. All remaining cows showed normal water consumption after the first day of exposure and did not experience any decrease in feed intake or health. While no significant difference in milk production occurred, a slight trend to lower production is evident in the data in this trial.
Studies exposing cows to electric shock at milking time have consistently demonstrated a behavioural response including nervousness, "dancing" and kicking off milk machines at current of 2 to 4 ma AC, applied as intermittent shocks. These studies do not indicate changes in hormones related to stress, milk ejection or milk production, nor do these short term studies support a decrease in milk production or udder health. The response of dairy cattle to stray voltage under field conditions has been reported to include nervousness during milking, refusal to enter the milking parlor, decreased feed and water consumption, poor milk let down and incomplete milking, increased milking time, increased somatic cell count and incidence of clinical mastitis and lower milk production. While research to date supports only the behavioural responses, it is likely that management practices on commercial farms and longer term exposure can cause behavioural responses to impact on production and health. As examples, failure to re-attach machines kicked off several times could lead to decreased production, and liner slips, caused by cows dancing about during milk could result in new mastitis infections. Longer term research under more commercial conditions are required to investigate these assumptions.
A longer term study examining the effect of continuous exposure to stray voltage in a tie stall barn has been conducted at New Liskeard College of Agricultural Technology. In the first phase of this trial, cows were exposed to 1.0 volt on stabling and water bowls for two three-hour periods between 5 and 8 a.m. and 5 and 8 p.m. daily. Voltage on stabling was 0.3 volts at all other times, to simulate the type of variation in voltage observed in the field. Analysis of observations on 31 cows in a cross over design including 28 day treatment and control periods, suggests no effect on behaviour, feed and water consumption, milk production, somatic cell count or reproductive performance. A second phase, using 2.5 and 0.75 volts has also yielded no observed effects on behaviour or measurements of performance.
In the third phase of the trial, cows were exposed to 5 volts in the two 3-hour "high" periods and 0.75 volts the remainder of the day. Results of this phase are included in table form. Few behavioural differences were noted, although treated cows urinated more frequently despite lower water consumption. It is noteworthy that drinking frequency was not different during high vs. low voltage periods. Treated cows consumed less water and produced significantly less milk protein, but differences were small. A difference of 1.1 kg in milk production approached significance (P-).1) lending the author to conclude that 5 volts was a "threshold" level for well managed tie stall herds. A field study of a commercial tie stall herd in New York State, repeatedly subjected to periods of voltage up to 2.0 volts, also concluded there were no effects from voltages in this range.
Despite the suggestion earlier in this paper that behavioural symptoms precede reduced performance, it is noteworthy that in this trial, behaviour is not affected at the 5 volt level.
Production is lower by an amount which only reaches significance for milk protein.
Measurements taken in the field, indicate that one of the potential explanations for the inconsistent response of dairy cattle to stray voltage is wide variation in electrical resistance related to housing conditions. Extremely high contact resistance from fixed stabling components to neck chains, from neck chains to the cow and from the cow to earth, especially in dry, well bedded barns, suggests a pathway resistance several times greater than 390 ohms. This insulating effect may explain why measured voltages in excess of 1.0 volt on stabling are not always associated with stray voltage symptoms. Generally, a behavioural response in the milking parlor where floors are wet has been more predictable.
In spite of a growing body of research, it would appear that a clear definition of the level of voltage which constitutes a problem for dairy cattle is still beyond our grasp. Currently, extension information in the United States recommends corrective action if voltage between cow contact points exceeds 0.5 volts, and in Ontario a level of 0.75 volts has been suggested. In view of recent research and experience, these guidelines are highly "sensitive" and would encompass nearly all problem situations, but not very "specific" in that many herds with this level do not exhibit stray voltage symptoms. A more "specific" guideline would be to encourage corrective action only in situations where these levels of voltage are present and behavioural (nervousness, etc.) symptoms are present. In a well managed tie stall situation, experience suggests no symptoms may be evident until voltage exceeds 4.0 to 5.0 volts between cow contact points.
In studies with swine, Minnesota research exposed growing pigs to varying levels of voltage on metal water nipples. Pigs showed a preference for drinkers with 0 volts from very low levels indicating a "perception" threshold of 0.2 volts and a pathway resistance from mouth to all hooves of 789 ohms. Drinking behaviour was modified at a level of 2.8 volts and water consumption declined above 3.6 volts. In a large study of swine in Quebec, pigs were exposed to 0, 2 and 5 volts from both metal drinkers and feeders to the pen floor, from 9 to 21 weeks of age. Very few changes in behaviour were observed. Daytime eating frequency was decreased at 5 volts in one 2-week period only and drinking frequency was decreased at 5 volts in restricted fed pigs. At 2 and 5 volts, pigs spent less time nibbling on the feeder. Feed intake and daily gain were lower in 5 volt pigs from 17 to 21 weeks only and this was not significant when assessed over the entire trial. At slaughter, there were no differences in carcass characteristics and gastric lesions or ulceration. A second trial at 0, 5 and 8 volts also found no impact of feed or water intake or rate of gain. Evidence from both these studies suggested that heavier pigs may be more sensitive. Subsequent studies of body impedance showed that impedance declined from 3500 ohms to 1000 ohms from 10 to 22 weeks in an inverse relationship with pressure exerted by the hooves. Impedance was lower on a wet floor than on a dry floor.
As with dairy cattle, these studies confirm a much higher tolerance for stray voltage than postulated earlier based on "perception" data. They also illustrate that sensitivity varies with the condition of animal contacts so that no single level of tolerance can be defined for wet and dry environments.
Clearly, any stray voltage attributed to fault current or high resistance neutral connections in the farm service should be dealt with by repairing faulty electrical equipment and wiring. Since these sources are not common, most tingle voltage problems will require additional corrective action.
A number of corrective devices and measures have been proposed to reduce or eliminate stray voltage from livestock facilities. In Ontario, the Ministry of Agriculture, Food and Rural Affairs and Ontario Hydro have cooperated in evaluating these measures and developing recommendations for Ontario livestock producers. During 1980-85, Ontario Hydro policy allowed for separation of the primary and secondary neutrals at the transformer serving the farmstead. This separation eliminated off-farm sources of stray voltage and reduced measured voltage between cow contact surfaces to a non-problem level in nearly all situations. Neutral separation was viewed as a temporary measure in that it reduced system grounding of the distribution system, posed a potential hazard for linemen and was viewed as unsafe in the event of a transformer failure. During this period, Ontario Hydros research department developed the tingle voltage filter, a saturable reactor which isolates the grounding system from current carrying conductors at the barn service entrance panel. The device saturates in the event of a fault current on the ground system. Until recently, the filter was manufactured by Hammond Manufacturing of Guelph Ontario, however they have discontinued production due to lack of demand for the product. The filter performs satisfactorily under fault testing and reduces tingle voltage levels by 76.7 to 99.7% in field studies. Proper installation requires complete separation of neutrals and grounding, therefore, installation by an experienced electrician is advisable. Installation of an optional indicator kit allows the herd owner to monitor filter operation. The tingle voltage filter has proven to be an effective solution for most dairy facilities with approximately 3000 units sold in Ontario. Since its introduction, farms with separated neutrals have been advised to install the device, and the neutrals have been reconnected. While no new filters are available today, most electricians can source used filters from farms that no longer have livestock. Ontario research by Chisholm assessing the effectiveness of the filter in isolating stabling from voltage spikes on the neutral show this device is slow to saturate and provides effective mitigation of such phenomena.
One commercial company currently addresses stray voltage by installing passive isolation devices in the individual grounding conductors to stabling, water lines, etc. While this approach usually involves more labour and cost than a filter installation, it is effective and has the advantage of eliminating rather than reducing the level between cow contacts.
An alternative solution, particularly applicable to milking parlors, is the installation of an equi-potential grid. The grid consists of a welded wire mesh, embedded in the concrete of the cow platform in the parlor and in other areas where cows contact bonded stabling or feeding or water devices. The mesh is bonded to the neutral, thereby raising all contact to the potential of the neutral and eliminating exposure to stray voltage. Equi-potential grids are required in new milking parlor construction under the Canadian Electric Code and are included in Canada Plan Service milking parlor plans. The grid offers the added advantage of improving system grounding and eliminating electric shock hazard for livestock on the grid from all sources including lightning. It may be necessary to include a transition consisting of a 140 cm long extension of the grid buried at a 45° angle to reduce front to rear hoof shocks when cattle step onto the grid. Grids are difficult and costly to retrofit existing barns or parlors and are usually a less practical solution to identified problems than the use of tingle voltage filters. In new construction of milking parlors or tie stall barns, the low cost of including a grid in the cow platform makes this a practical preventative measure.
Other solutions such as neutral separation devices, isolation transformers and active suppression devices are also available, but are less practical than the filter or grid. Neutral separation devices are comparable in cost to the filter and do not eliminate voltage due to secondary neutral currents. Isolation transformers are costly, do not eliminate on-farm sources and may restrict future increases in power usage. Active suppression devices are very effective, but their extremely high cost makes them totally impractical.
One company which currently promotes active suppression devices, also recommends use of low voltage, low current electrodes in receiver jars to eliminate this source of stray voltage. As indicated earlier, the pathway through milk has a well defined, high resistance and is not a source of shock potential to cows. Add to this the large gap in the jar itself, the use of glass jars on most farms, and it becomes apparent that concern about receiver jar electrodes as a source of voltage is totally unjustified.
Certain commercial interests have also developed new theories, postulating effects other than electric shock from currents measured in the environment of the animal. In these theories, current flow in stabling, in equi-potential planes and in the earth around the cow, reduces animal performance even when there is no measurable potential difference across cow contact points and therefore, no potential for shock. Such theories should not be regarded as relevant to stray voltage as defined by research to date, as there is neither a sound theoretical basis nor research nor field experience to support these claims.
Although the science of stray voltage mitigation is quite straight forward, a lack of widespread demand for assistance, staff reductions at utility companies and shifting emphasis in government extension and variable levels of skill and experience among rural electricians may make it difficult to access qualified technical help. Unfortunately this discipline has also attracted a significant number of consultants with new theories, and mitigation approaches that are not supported by research. Hopefully information in this document can be helpful in critically evaluating the advice and service offered. In the experience of the author, a properly equipped and knowledgeable electrical contractor should be able to resolve any farm stray voltage issue with one or more tingle voltage filters and 2 to 10 hours of installation labour. Solutions that cost more than $1000 to $2000 per farm should be viewed with suspicion.
The following step-by step procedure is intended to help isolate the causes of a stray voltage problem. A form for recording the data as well as notes on how to interpret the data are included. The tests may take several hours to conduct. However, the entire procedure needs to be completed to determine if a problem exists and what the cause or causes might be. The test suggest the use of a clamp-on ammeter. The ammeter readings are optional for preliminary screening problems.
After establishing an isolated ground rod and connecting the voltmeter between the ground rod and the neutral bar of the service entrance panel, read the N-E voltage at the barn.
Record of Results: Voltmeter Reading (AC volts), Time
Interpretation: The voltmeter will now read the N-E voltage at the barn. This voltage is measured rather than voltages in the milking area itself because generally it is the maximum which would be expected between any two points in the Milking area, unless a fault exists.
N-E voltage without the barn load: Open the main disconnect at
the barn service entrance.
Record of Results: Voltmeter Reading
Interpretation: No load is operating in the barn at this time. However, the neutral to the barn is not disconnected. Any voltage in the barn at this time is being transmitted to the barn through the neutral or grounding system and originates somewhere else.
Removal of loads from other farm buildings. Leaving the main disconnect at the barn open, record the N-E voltage at the barn after opening each of the other service entrances on the farm. Leave the service disconnects open until all have been disconnected.
Record of Results: Service Disconnecte, Voltmeter Reading
Interpretation: After each service entrance is disconnected, the N-E voltage at the barn should drop slightly if there are any loads operating on that service entrance. If the voltmeter reading at any step is relatively high (above 0.5 volts) and drops to a much lower value (less than 0.2 volts) when the service entrance is disconnected, the loads on that service entrance should be checked out later. This drop in voltage could be caused by a faulty load on that service entrance or it may be the result of a heavy load on the entrance at the specific time.
Complete removal of farm load. Open the main disconnect to the farm and record the N-E voltage at the barn. Be sure the well is also disconnected if it is powered ahead of the main disconnect.
After Step 4 is completed reconnect the main service and all building services.
Record of Results: Voltmeter Reading
Interpretation: The voltage recorded at the barn when all services are open is due to N-E voltage on the primary neutral created by loads at other locations on the main distribution system. When the main disconnect is opened the voltage reading should be the same as when all building services were disconnected.
Checking 240-volt loads in the barn: Place a clamp-on ammeter around the neutral to the barn service. Be sure no 120-volt loads are added or dropped during this test. Record the voltmeter and ammeter reading after each of several 240-volt loads are added to the previous load. Also read the voltmeter and ammeter as each load is turned off in reverse sequence.
Record of Results: Load Added Voltmeter Reading, Ammeter Reading
Interpretation: The increase in neutral-to-earth voltage as each load is added is due either to the increase in primary N-E voltage as a result of the increased load or to faulty equipment on that circuit.
If any 240-volt load causes a current flow in the secondary neutral to the barn (as indicated by the clamp-on ammeter) it is a result of interconnected 120-volt loads or ground faults in the equipment. Very slight changes in neutral current may be detected as a result of the increased N-E voltage forcing some current through the electrical system grounds at the barn. These will be very small and are not an indication of ground faults in the equipment.
Checking 120-volt loads in the barn. Open all 120-volt circuits in the barn. Record the voltmeter and ammeter readings as each of the 120-volt circuits is reconnected and the loads on that circuit are operating. Carefully observe the effects of starting and stopping 120-volt motors. They can cause serious N-E voltage when starting.
Record of Results: Circuit Number, Loads, Voltmeter Reading, Ammeter Reading
Interpretation: The secondary neutral current to the barn (read by the clamp-on ammeter) and the N-E voltage readings will increase and decrease as the unbalanced load on the secondary neutral to the barn changes. If the N-E voltage increases significantly (perhaps 0.3 volts or higher) with a maximum unbalanced load on the barn neutral, the voltage drop in the neutral may be causing problems. The problems may be a high neutral resistance created by poor connections or the resistance of the wire itself. Improving connections, better balancing of the line-to-earth loads, and or a larger neutral wire may help relieve the problem. Making sure the current in the barn neutral is minimized during milking (by selection of offsetting 120-volt loads) may help solve the problem. It is possible for the N-E voltage to decrease with an increase in secondary neutral current. This is caused by the voltage drop in the secondary neutral counteracting (subtracting from) the primary N-E voltage. This occurs when the unbalanced current is created by loads on the 120-volt leg that is 180 degrees out of phase with the primary voltage.
Circuit checks for other farm buildings.If in Step 3 one of more of the other building services seemed to produce an excessive voltage repeat Steps 5 and 6 for that building.
Milking time monitoring. Have someone watch the voltmeter throughout the milking time and periodically record the readings, both the peak values and static (steady) values. (You will probably require additional space for recording this data).
Record of Results: Peak, Voltmeter Reading Static, Time
Interpretation: Pay particular attention to major changes in fluctuations in the readings. These may occur rapidly and may last only a short time. Close attention is necessary to observe these changes. Starting of motors is the most common cause of short-term peaks.
Isolated system testing. Repeat the procedure outlined in cooperation with the power supplier after its employees, under the direction of their supervisors or engineering consultants have disconnected the bond between the primary neutral and the secondary neutral at the transformer. The disconnection of this bond is not possible with single busing transformers in common use today and requires changing transformers. This step requires disconnecting the bond only; it is critical the primary neutral and secondary neutral connections to the transformer remain intact and are not disconnected.
Interpretation: After the bond between the primary and secondary neutrals has been disconnected, there should be no change in the N-E voltage at the barn when the 240-volt loads are operated. If this voltage increases with these loads, there is either an electrical fault in the equipment or the voltage on the primary neutral is feeding back onto the secondary neutral through the earth or some other electrical connection. (Primary and secondary neutral systems have not been isolated). If the tests outlined show an N-E voltage problem, the results should indicate whether the problem originates on the farm, off the farm as a result of an excessive primary N-E voltage, or a combination of the two.
For more information:
Toll Free: 1-877-424-1300