A Charged Debate: The Stray Voltage Puzzle
Since the 1960’s producers, dairy authorities, electrical professionals and researchers have been investigating stray voltage as the potential culprit of poor production and health. After extensive review of feeding, milking, hygiene and management procedures, for some dairies stray voltage seems like the only possible cause for problems with elevated SCC and mastitis.
If stray voltage does cause these problems, why can’t controlled experimental studies substantiate these effects? Lack of concrete evidence may lead to dismissive attitudes from authorities and power companies, but for many farmers stray voltage is a very real problem.
Stray voltage is defined as a low level (less than 10V) of voltage present across two points in which a current flow is produced when an animal touches both points simultaneously. Current flow (measured in milliamps (mA)) is used as the standardized measurement instead of contact voltage due to the variable resistance from each cow’s body and the path the electricity takes between the contact points. Common contact points include water bowls, milking equipment and wet floors. Stray voltage in levels high enough to impact cows is usually caused by1:
- Primary neutral current flowing to the farm because of the neutral connection of two systems at the transformer
- Unbalanced load: secondary neutral current originating from 120V on-site equipment
- Fault related currents from primary, secondary of neighboring services to neutral, ground, stabling or earth
Environmental factors such as placement of wells, ponds and a high water table may amplify the effects.
A 1993 report in The Iowa State University Veterinarian places the cost of stray voltage at $55 million per year for replacement animals and $125 million per year for production losses2. A 2004 article in Farmer’s Weekly estimates that 31% of dairies in New Zealand’s South Island and 67% in Wisconsin have problems with stray voltage3.
The vast majority of scientific research has concluded that stray voltage has insignificant (if any) effects on milk production, milk composition, SCC, mastitis and other health problems. The most significant effect found in controlled studies was decreased water consumption when water bowls were used as contact points. Most cows acclimatized after 24 hours, but a few cows refused to drink for up to 36 hours after which the voltage was removed.
The few studies that did show a yield decrease after exposure to voltage did not demonstrate a reduction in water consumption, meaning that some other factor must have been responsible for the yield drop4.
Some limitations of many studies that were reviewed is that the experimental period was only over several weeks, only one study could be found that investigated the effects of stray voltage over a full lactation. It is also possible that farms with the more severe problems are experiencing voltage levels above what researchers can ethically experiment with.
While research does not agree on the direct impact of stray voltage to production and health, there are thresholds at which it is generally agreed that behavioral effects are seen. Cow’s exhibit signs that they can perceive stray voltage at levels from 1-3mA and display avoidance behaviors such as refusing the drink and kicking off milkers at 4-6mA.
A plausible explanation for stray voltage causing elevated SCC and mastitis is that cows displaying avoidance behaviors in the parlor such as kicking and restlessness cause liners to slip, resulting in an ineffective milk letdown, longer milking times or incomplete milkout.
Many studies have shown increased levels of the hormones cortisol and epinephrine after exposure to voltage, which block the release of oxytocin and subsequently impede milk letdown. These situations are well-known to increase the risk of mastitis and elevated SCC. Therefore, it may not be that these problems are directly caused by stray voltage, but are secondary to the avoidance behaviors exhibited when cows are exposed.
There are some ways to mitigate the amount of stray voltage reaching your cows. Some may be more effective than others depending on your situation.
- Voltage reduction involves removing bad connections and faulty loads, improving or correcting writing and grounding as well as controlling leaky currents by cleaning, reinsulating and grounding.
- Active suppression is achieved through a nulling device or voltage filter installed on the main electrical lines. Although there is no need to alter the existing electrical system this method can have high installation and maintenance costs as well as potentially overlooking the problem source.
- Gradient control is the installation of an equipotential plate through conducting rods in the floor and proper metalwork bonding to better ground electricity.
- Isolation is the electrical separation of the grounded neutral system at either the building being serviced or the distribution transformer through conventional spark gaps, saturation reactors or solid state switches
If you have had problems with stray voltage, please join the discussion and share your experience and solutions. The more people that are communicating about this issue, the closer we will get to understanding how stray voltage causes health and production problems, why experimental studies cannot replicate real world situations and uncovering the factors that make some farms more susceptible than others.
About the Author
Anna Schwanke is an undergraduate student at the University of Guelph, Ontario. She is responsible for researching and writing about a wide variety of topics related to dairy cow welfare and management for Dairy Quality Inc. The 10 years she spent living in Australia, as well as her love of travelling, give her a firsthand viewpoint of issues facing the international dairy community. She plans to graduate from the University’s College of Physical & Engineering Science in 2019 and pursue a career in the Life Sciences or Agriculture industry.
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