Pork producers are discovering something about electricity that dairymen have known for years — stray voltage hurts production.
The term is a misnomer, says agricultural engineer Larry Jacobson of the University of Minnesota. He prefers neutral-to-ground voltage. Basically, it occurs when an animal comes between two surfaces that are at different voltage. “One isn't as well grounded, so they are at different potentials,” he explains. “When the animal touches something like a water nipple, current goes through the animal.”
Swine veterinarian Amy Woods, Rensselaer Swine Services, Rensselaer, IN, says stray voltage is a difficult concept and hard to prove. “We have cases where gut feeling says it may be involved, but it is usually diagnosis by exclusion.”
Woods discussed a stray-voltage case at the annual Swine Disease Conference for Swine Practitioners in Ames, IA, recently. An exceptionally high-producing 1,800-sow herd was suffering mysterious sow deaths and high preweaning mortality from poorly lactating sows.
The diagnosis was “puffer sow” syndrome, a strange malady evidenced by rapid respiratory rate, muscle weakness and high fever. Sows would collapse and die as a result, Woods believes, of some type of stress, most commonly the start of farrowing.
Affected animals were necropsied, but there were never significant findings. Many sows were ketotic, but there were no major abnormalities on blood counts. Serum chemistries did show sows tended to be hypoglycemic and magnesium levels were often very low.
Treatments included Flunixamine, cool running water to decrease fever and injections of Cal-Dex or Cal-Phos, which provided supplemental magnesium. Epsom salts were run through the water in gestation at 4 lb./gal. of stock solution that was metered into the drinking water at 1 oz./gal. These interventions helped, but the farm's sow mortality still averaged nearly 13.5% and was rising. Preweaning mortality was 3% higher than normal.
When the sow death rate hit 28% in July of 2004, Agrivolt, a Canadian company specializing in stray voltage, was called in to investigate.
According to Jacques Dion, president of the Quebec company, 70% of electrical systems in North America use the ground as the return path of current because it's safer and more reliable. Livestock are parallel with the grounding network, so whatever is flowing back includes a portion of current going through the animal.
“There's nothing wrong with this, providing the voltage doesn't exceed the animal's sensitivity threshold,” he says. “In the pig, it is quite low, but as animals are pushed to maximum performance, they are becoming more sensitive to voltage fluctuations. The electrical load on farms is also increasing, and the return has to go somewhere. We see more and more current flow underground, and that's where problems start. Grounds are not designed to return electricity, but to handle faulty current.”
Voltage Variance Tested
Agrivolt's first step was to record variances in voltage from the farm's electrical system over a three-day period. A sensitivity threshold of 1.2 volts was set for the facility, which included motors from fans, pressure washers, cool cell pumps and clothes dryers. The evaluation showed the farm had a standard peak level of 6.4 volts and spikes of 10.1 volts when motors turned on.
“That is an amazing range of quantity of current,” says Dion, “and enough to create stress.” Current causes a tingling sensation and likely occurred when crated sows touched nipple waterers or feeders, causing them to go off feed.
The farm's managers were skeptical of Agrivolt's findings. The facility was only a year old and wired to code. And, changes to the network were expensive, particularly since the transformer was moved 75 ft. from the original spot due to a driven ground nearby.
“My point to them was if they have control over factors such as health and nutrition, we could control and deviate current on wires instead of grounding,” Dion explains. “Equipment and expertise amounted to about $43,000 to neutralize the problem, but within a short period, there was major improvement.”
When the switch was flipped on the revamped system in August of '04, the herd had slipped to 27 pigs/sow/year, down from 28. The impact on death loss and piglet mortality was immediate, according to Woods (see Table 1). The puffer sow syndrome decreased dramatically and sows started eating and milking better.
Past research shows that pigs are sensitive to electricity at about 5 volts, Dion continues. He's convinced pigs are becoming less resistant as productivity increases. “Today, we're dealing with 2 or 3 volts before animals are impacted.” (The correct term is amperage, but voltage is commonly used.) Stray voltage is typically only a volt or two.
Woods agrees that stray voltage represents another stress to sows that are already pushed to extremely high productivity. She did not feel it was a direct cause of the puffer syndrome; it just sent sows over the edge. Older sows, Parity 3 and higher, were also affected more than younger, more tolerant animals.
Voltage is a function of resistance, due to Ohm's law, which states that current, or amperes, times resistance, or ohms, equals volts. Woods says the Canadian Plan Service suggests a finisher pig has a resistance of about 930 ohms.
Some animals can detect current as low as 2 milliamperes, which according to Ohm's law would take only 0.72 volts to reach for a cow, but 1.86 volts for a pig, she says. If the animal is wet, resistance is much lower and the animal becomes an even better conductor. Humans have a much higher resistance than animals.
Monitoring equipment was installed at the farm to detect stray voltage from faulty wiring, bad motors, electrical shorts, etc. An alarm sounds at a predetermined voltage threshold and the source of the problem is traced.
The system is on-line through telephone hookups with Agrivolt, and was tested when a cool cell pump went out and the alarm went off. Water in an outlet was also sending stray voltage. “If a defective wire leaks to the ground, this farm knows right away to fix it. Nothing is flowing back to the animals,” Dion points out.
Producers need to focus on regular maintenance and monitoring of electrical devices and motors to be sure they are working properly and wiring is well insulated, says Woods. “Stray voltage is starting to get people's attention. If suspected, call electrical experts familiar with stray voltage.
“Keep in mind, stray voltage occurs intermittently, so it often goes unnoticed. It is impossible to eliminate all sources of stray voltage on a farm, but it can be minimized,” she adds.
Most farms have had an ongoing problem for years, adds Dion. Producers don't know what they're losing in productivity. In the past, they've taken for granted higher death rates or tail biting problems because they've always had them. He figures 5-10% of his business is in swine facilities.
Years ago, Dion recalls, they would deal with 20 to 25 circuit breakers on a swine operation. Today, operations have 140 to 150 circuit breakers. “Electricity has to be managed today, and the tools are available,” he says.
For more information on neutral-to-ground (stray) voltage issues, contact Agrivolt, Inc. at (800) 463-3486 (push 9 at the prompt for English), or www.agrivolt.com.
Stray Voltage Defined
Stray voltage is the voltage difference between two contact points. When an electrical conductor, such as an animal, connects these points the current flows through this completed circuit. It comes from the neutral-to-earth voltage that develops as current flows through the ground at points where the system is grounded. Any neutral-to-earth voltage within the system can be transferred to any grounded objects.
Stray voltage can also be generated by the power supplier so it comes into the farm on the primary neutral wire, or it can be caused on farm by faulty wiring, worn insulation, loose connections, improper grounding, shorts in motors or unbalanced 120-volt loads on the circuits.
Stray voltage can also 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 possible route. Animals can become a part of that path.
|Monitor Performance||Jan. 4||Feb. 4||Mar. 4||Apr. 4||May 4||June 4||July 4||Aug 4||Sept. 4||Oct. 4||Nov. 4||Dec. 4||Total|
|Pigs weaned per sow||11.1||11.2||11.2||11.4||11.0||10.8||10.6||10.4||Stray Voltage Correction August 2004||10.7||11.1||10.7||11.6||10.9|
|Ending female inventory||1,910||1,863||1,814||1,827||1,849||1,788||1,815||1,767||1,826||1,846||1,872||1,871||1,871|
|Sow and gilt deaths||16||25||19||11||22||19||43||23||5||7||8||6||204|