The amount of stray voltage running through a farm can change greatly as motors on fans and other electrical equipment start up or turn off.
Pork production is a dynamic and challenging endeavor. Any number of inputs can affect a herd"s productivity.
Amy Woods, a swine veterinarian with Rensselaer Swine Services, PC, Rensselaer, Ind., offers a case study that demonstrates this phenomenon.
It starts off with sows on a farm that suffered from a strange "puffer-sow" syndrome. Sows weren"t eating normally or milking well, causing high pre-weaning death loss, as well as rising sow-mortality rates.
The producer and veterinarians investigated many nutritional, pathological and metabolic issues, all of which proved to be contributing factors that offered some treatments. However, the main factor was eventually identified as stray voltage.
While stray voltage gets attention in the dairy industry, it rarely makes the radar screen in pork production. Monitoring productivity in terms of milk yield is essential in a dairy barn, where even a slight drop raises suspicion. But it"s not as easy to quantify it in the sow herd.
So, let"s take a look at this sow herd"s dilemma.
The farm is a 1,800-sow, two-site operation built in 2002. The first sows farrowed in January 2003.
However, a year later, a puffer-sow syndrome surfaced in the farrowing house. Affected sows had rapid respiratory rates, muscle weakness (especially in the rear) and exhibited 106' F and higher temperatures. Sows often collapsed and died. The syndrome affected all sows, although it was more common in parity three or older sows.
Several affected sows were necropsied. Diagnostic work-ups found nothing significant. Ironically, most affected sows had large litters. Many also were found to be ketotic. The veterinarians performed numerous biochemical profiles and complete blood counts, but found no major consistent abnormalities.
However, serum chemistries did show that affected sows tended to be hypoglycemic and have an elevated creatinine, notes Woods. They often were low on magnesium. "All affected sows had a high creatine kinase-- many greater than 100,000 UIL (reference range: 24 to 225 UIL) which may be due to muscle damage on the weak, downer sows," she adds.
Based on those findings and the sows" clinical signs, the herd-health team tried many treatments. Sows were treated with flunixin meglumine and cool running water to reduce the fevers. They received supplemental magnesium. Some animals also responded to injectable thiamine.
Epsom salts were run through the farrowing house water supply at 4 pounds per gallon of stock solution (proportioned at 1 oz. per gallon) as an additional magnesium source to help prevent hypomagnesaemia.
The treatments saved many sows, but the syndrome continued, and many sows still died. The farm"s sow-mortality rate averaged 13.5 percent during this period, with a spike exceeding 28 percent in July.
Stray voltage is often traced to feeders and waterers, where it disrupts consumption and spirals the animal into herd health problems.
Many sows went off-feed and didn"t lactate well. The farm"s management conducted aggressive piglet fostering and milk replacer programs. Still, weaning weights dropped and pre-weaning mortality ran 3 percent higher than normal.
The question of stray voltage eventually surfaced. Agrivolt (now Nuvolt, (800) 463-3486), a company that works exclusively with stray voltage in agricultural facilities was called in to investigate. Based in Quebec, Canada, company personnel conducted a three-day, on-farm evaluation.
They looked at how much stray voltage could be detected throughout the day, including variances when all motors (fans, pressure washers, cool-cell pumps and so forth) were running, says Woods.
They set a sensitivity threshold of 1.2 volts for livestock facilities. The farm had a standard peak level of 6.4 volts, and a level of 10.1 volts when motors started up.
Agrivolt personnel changed all of the grounding in the barns and initiated a system to eliminate any stray voltage coming in on the primary neutral or through the ground. They installed monitors to detect any stray voltage that occurs within the farm from faulty wiring, motors gone bad, electrical shorts and such. The monitor alarm was set to go off at a predetermined threshold. The stray voltage can then be traced back to the source and corrected.
Installed in August 2004, the monitor made an immediate impact on sow and pre-weaning mortality. Sows started eating and milking better.
"Stray voltage was not likely the direct cause of the puffer-sow syndrome, but it added yet another stress," notes Woods. "It"s easy to relate stray voltage to a drop in feed and water consumption since sows likely felt it as they contacted the feeder or water nipple." It doesn"t take much of a jolt to teach a sow to back away.
Too often stray voltage is diagnosed by exclusion. For clarification, it is the current flow not the voltage that affects livestock. Voltage is a function of the animal"s resistance due to Ohm"s law, which states that current (amperes) x resistance (ohms) = volts.
The Canadian Plan Service suggests that a finishing pig has a mouth-to-hoof resistance of about 930 ohms; a cow has a resistance of about 360 ohms, notes Woods. Some animals can detect current as low as 2 mA (milliamperes). According to Ohm"s law, it would take only 0.72 volts to reach that current level for a cow, but 1.86 volts for a pig. If an animal is wet, its resistance is much lower. Humans have a higher resistance, so we normally cannot detect voltage levels that affect animals.
Stray voltage is the voltage difference between two contact points. "So, when an electrical conductor, such as an animal, connects those points the current flows through the completed circuit," says Woods. "Stray voltage comes from the neutral-to-earth voltage, which develops as current flows through the earth at points where the electrical system is grounded to the earth."
Any neutral-to-earth voltage within the system can then be transferred to any grounded objects within the farm. Stray voltage can be generated by the power supplier, coming into the farm on the primary neutral wire, or it can be generated on the farm by worn wiring insulation, loose wiring connections, improper grounding, electrical shorts in motors or unbalanced 120-volt loads on circuits, says Woods.
Stray voltage also can travel through the earth from neighboring facilities. "All electricity that comes into a farm strives to travel back to the power source by the easiest route possible. Since animals act as good conductors, they can become a part of that path," she adds.
Detecting stray voltage can be problematic. "It sounds simple to use a voltmeter to determine the voltage difference between two animal contact points, such as the feeder and the floor," says Woods. "Another crude method is to apply the point-to-ground measurement method."
To do this, a voltmeter, using a well-insulated wire, is connected between an animal contact point within the barn and a ground rod driven at least 30 feet away from any barns, electrical grounds, water pipes or grounded electrical equipment, she notes.
Still, neither method provides a truly accurate stray-voltage picture because you"re checking at a single point in time. The amount of stray voltage running through a farm changes greatly as motors start up or turn off.
"Once the producer had stray-voltage monitoring equipment installed, it was easy to observe the voltage present," says Woods. "No surprise that it increases significantly in the summer as more fans and cool-cell pumps turn on."
It is impossible to eliminate all stray-voltage sources, but there are ways to try to minimize it. The electrical company may be able to help minimize off-farm sources. In this farm"s case, the electrical transformer on the ground was moved 75 feet away from its original location due to a driven ground near the transformer.
On-farm efforts need to focus on regular maintenance and monitoring of all electrical devices and motors, to ensure that they are in proper working condition that all wiring is well insulated, says Woods.
Anytime stray voltage is suspected, contact an experienced electrician to help determine if it"s a problem and to help correct it.
No question, stray voltage is a real issue that occurs in swine facilities. However, detection can be difficult, requiring off-farm and on-farm sources and cooperation to address it.