Stray voltage is a result of grounded electrical currents entering and then exiting a nearby object in a feedback loop manner. Some of the common causes that can occur is when a wire is too small to bare the current load or if the wire is damaged allowing the electricity to go into the ground. Stray voltage can also be caused when power lines are “leaking”, and currents are flowing into the ground.
Stray voltage is defined as less than 10 volts between two points contacted by an animal (USDA, 1991). Stray voltage on a dairy farm is important to dairymen as it can negatively affect milk production and overall efficiency. Some research has shown that if there is stray voltage on a dairy farm and it is corrected, there can be roughly 500 kg/cow/year increase in milk production, however, improvement in milk production is not always seen (Rodenburg, 1998).
Electrical current flows through the cow when she contacts two points that have a voltage potential between them (example, water trough and cow’s hooves in Fig. 1). The cow has “completed the circuit”. The direct effect of electrical current flow through the cow include mild behavioral responses, muscular contractions, or strong behavioral reactions depending on the current level, animal pathway, duration, and other factors. (Progressive Dairy, 2015; Reinemann, 2009; Rodenburg, 1998). Normal cattle behavior may change as a result of exposure to stray voltage. For example, if cows are exposed at the watering trough, they may choose to stop drinking water or drink at a different watering trough. Another example is cows may avoid walking in certain areas or eating at the feedbunk if they have previously been exposed to stray voltage at that location. This avoidance behavior is an indirect effect of stray voltage.
How do cows “resist” stray voltage?
Resistance is a measurement of how able an object is to “resist” the electrical current flow through it. A rubber mat is an example of a high resistance material and a copper wire is an example of low resistance material. At a given voltage, the current flow will be much higher through the copper wire than through the rubber mat. The electrical resistance dairy cow includes both the cow’s body and the resistance of the contact points (i.e. feet on concrete and muzzle in drinking trough) (Fig. 2).
The effects of stray voltage on a dairy cow can differ depending on the body resistance of the cow, the size of the contact area, pressure on the contact area, wet vs. dry haircoats, wet vs. dry hooves, frequency of occurrence, or pathway of voltage through the cow (e.g. mouth to hooves or rear hooves to front hooves; Reinemann, 2009).
How do we influence the electrical resistance of dairy cattle?
The cow’s relative risk of exposure to stray voltage varies based on the cow’s daily time budget and our dairy housing practices. Cows typically spend 3 to 5 hours/eating, 2 to 3 hours/day standing with social interactions, 2.5 to 3.5 hours/day outside the pen traveling to/from milking center, and ½ hour/day drinking water (Grant, 2009). Cow electrical resistance at the feed bunk and in the parlor will be lower if her hair coat is wet from rain, from using fence-line soakers for heat stress abatement or water spray in the parlor. Using rubber mats at the feed bunk, in travel lanes, and in the parlor will increase the electrical resistance by adding a high resistance (poor conducter) material to the pathway through the cow. Open lot housing without shades will have a greater risk of wet haircoats than open lots with shades. Free stall housing with gable roofs will minimize the risk of wet haircoats from precipitation but have a higher initial investment. Flushing systems will tend wet feet and decrease cattle resistance.
At the water trough, the use of non-metallic watering devices, avoiding the use of electric heating elements (if possible), and providing several watering locations per pen can help to reduce the effects of stray voltage (if present). Additionally, at the feed bunk and water trough, cows will be standing on wet concrete or in manure and/or urine which will lower the electrical resistance of a cow.
Take home message
Although stray voltage is often disregarded it can have serious effects on cattle performance. Given that the contact points as well as conditions on a dairy operation have effects on a cow’s electrical resistant it is important to keep in mind areas that are susceptible to stray voltage. If there is a belief that there may be stray voltage, then a consultant should be contacted to evaluate and measure.
Jennifer A. Spencer, Ph.D.1, Juan Piñeiro, DVM, Ph.D.1, Sushil Paudyal, Ph.D.2 Assistant Professor & Extension Dairy Specialist1
Assistant Professor2 Texas A&M AgriLife Extension Service1 Department of Animal Sciences1,2 The Texas A&M University System1,2
Assisted Expert: Rick Norell, Ph.D. Professor, Extension Dairy Specialist Department of Animal Sciences Idaho Falls Research and Extension Center University of Idaho