Editor’s note: This case study was pre-sented at the 2005 Iowa State University Swine Disease Conference for Swine Practitioners by Amy L. (Carroll) Woods, DVM, a swine veterinarian with Rensselaer Swine Services, PC,
Swine production is a very dynamic operation in which there are numerous input factors affecting the productivity of the entire herd. This case demonstrates this phenomenon very well.
The sows on this farm were suffering from a strange “puffer sow” syndrome, leading to a high sow death rate, and they were also not eating normally or milking well, resulting in a high pre-weaning mortality.
Many nutritional, pathological and metabolic issues were raised and investigated in an effort to diagnose the causes. All of these issues proved to be contributing factors and subsequently led to the development of some symptomatic treatments. However, one of the main contributing factors was found to be an environmental mechanical issue -- stray voltage.
The effects of stray voltage are well studied and documented in the dairy industry, but this issue gets much less attention in swine production. In the dairy industry, it is very easy to monitor productivity in terms of milk yield. Just a slight drop in milk production can raise suspicion of a problem. This is not as easy to quantify in the pork production industry.
This farm is a 1,800-sow, two‑site operation that was built new in 2002. The first sows farrowed from this new unit in January 2003. The start‑up on this farm went very smoothly, and the farm has continued to have above average productivity.
However, a year after the first sows farrowed, they started experiencing a puffer sow syndrome near the time of farrowing. The affected sows had a very rapid respiratory rate, muscle weakness (especially in the rear) and exhibited temperatures of 106°F and higher. The sows would eventually collapse and die.
This syndrome was observed across all parities, although it was more common in parity three and older animals. Some type of stress on the animal would initiate it. The most common stress was the start of the farrowing process. However, in many cases, sows suffered from this syndrome after being moved within the barn or even after receiving a prefarrowing scour vaccine.
Numerous affected sows were necropsied. Full diagnostic work‑ups were performed, but there were never any significant findings. Most of the affected sows did have very large litters of pigs. Many sows also were found to be ketotic. Numerous biochemical profiles and complete blood counts (
However, the serum chemistries did yield some significant changes. Affected sows tended to be hypoglycemic and have an elevated creatinine. They also often were very low on magnesium (Mg). All affected sows had a high creatine kinase (CK), many over 100,000
Based on these findings and the clinical presentation of the animals, many symptomatic treatments were tried. Sows were treated with Flunixamine (flunixin meglumine,
Epsom salts were run through the water in farrowing at 4 pounds per gallon of stock solution (proportioned at 1 oz. per gallon) as an additional Mg source to aid in prevention of the hypomagnesaemia.
These treatments saved many sows, but the syndrome continued. Even with the most aggressive treatment, many sows still died, and the farm’s sow mortality rate averaged nearly 13.5 percent during this time period, with the mortality increasing to more than 28 percent in July.
It is easy to relate stray voltage to a decrease in feed and water consumption in sows since the sows likely feel the stray voltage when they contact the feeder or water nipple.
In addition to the puffer sow syndrome that plagued this farm, many sows were off‑feed as well. Sows did not lactate well, resulting in lower weaning weights and much higher pre-weaning mortality rates.
The farm has very good management, and farm personnel implemented aggressive fostering and milk replacer programs in response to the poor lactation. Even with these efforts in place, pre-weaning mortality was nearly 3 percent higher than normal.
Eventually, stray voltage was investigated on this farm by calling in Agrivolt (phone:
They evaluated how much stray voltage could be detected throughout the day, including variances seen when all motors (fans, pressure washers, cool cell pumps, etc.) are running. They set a sensitivity threshold of 1.2 volts for livestock facilities.
After this extensive evaluation, it was found that this farm had a standard peak level of 6.4 volts and a peak level of 10.1 volts with motor start-ups. With this information in hand, the farm elected to pursue correction of the stray voltage in the unit.
The Agrivolt Company changed all of the grounding in the barns and put in place a system to eliminate any stray voltage coming into the farm on the primary neutral or through the ground. In addition, monitoring equipment was installed to detect any stray voltage that arises within the farm from faulty wiring, motors going bad, electrical shorts, etc.
The monitoring equipment has an alarm that can be set to go off at a predetermined voltage threshold. The stray voltage can then be traced back to the source and corrected.
The stray voltage control and monitoring equipment was installed in August 2004. This made an immediate impact on the sow death loss and pre-weaning mortality. The puffer sow syndrome, although still present occasionally, decreased dramatically and the sows started eating and milking better.
In this case, stray voltage is likely not the direct cause of the puffer sow syndrome, but it represents another stress on these sows that are already pushed to the limit due to their high productivity levels.
It is easy to relate the stray voltage to a decrease in feed and water consumption since the sows were likely feeling the stray voltage when they contacted the feeder or water nipple. As a result, the sow’s milk yield suffered, and pigs did not perform as well.
Stray voltage is most often a diag-nosis by exclusion. The impact of stray voltage on swine does not get much attention, but a Canadian study did show that daily feed intake and average daily gain were significantly decreased when pigs were exposed to increasing levels of voltage.
Stray voltage is an issue emphasized in the dairy industry but it is often overlooked in the pork industry.
The dairy industry is well aware of the ramifications of stray voltage. The typical clinical signs of a stray voltage problem include reduced appetite, lower water consumption, inadequate milk production, mastitis and behav-ioral changes such as agitation or avoidance.
It is actually the current flow, not the voltage that affects livestock. The voltage is a function of the resistance of the animal, due to Ohm’s law, which states that current (amperes) X resistance (ohms)=volts.
The Canadian Plan Service suggests that a finisher pig has a mouth‑to‑hoof resistance of approximately 930 ohms, compared with a cow that has a resistance of about 360 ohms. Some animals can detect current as low as 2 mA (milliamperes), so according to Ohm’s law, it would take only 0.72 V to reach this current level for a cow, but 1.86 V for a pig. If an animal is wet, the resistance is much lower, and the animal becomes an even better electrical conductor. Humans normally cannot detect the voltage levels that affect production in livestock because humans have a much higher resistance than animals.
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. Stray voltage comes from the neutral‑to‑earth voltage (
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.
Detecting stray voltage becomes very problematic. In theory, it sounds very simple to use a voltmeter to determine the voltage difference between two animal contact points, such as the feeder and the floor.
Another crude method of stray voltage detection 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.
However, neither of these methods truly works well to provide an accurate picture of the stray voltage situation on the farm. It is difficult to get an accurate picture of the stray voltage present by checking at a single point in time.
The amount of stray voltage running through a farm is a dynamic issue and changes greatly as motors on fans, etc., start up or turn off. After the installation of the stray voltage monitoring equipment on this farm, it is easy to observe the voltage present, and it increases significantly in the summer due to the number of fans and cool cell pumps in operation.
The amount of stray voltage running through a farm can be dynamic issue that changes greatly as motors on fans and other electrical equipment start up or turn off.
Lessening stray voltage
It is impossible to eliminate all sources of stray voltage on a farm, but there are many ways to attempt to minimize it. The electrical company may be able to help minimize off‑farm sources of stray voltage. In this 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 be focused on regular maintenance and monitoring of all electrical devices and motors to ensure that they are in proper working condition and all wiring is well insulated.
When stray voltage is a concern within a farm, an electrician familiar with working with stray voltage should be contacted to help determine if stray voltage is a problem and to help correct it.
Stray voltage is definitely a real issue that must often be dealt with in livestock facilities. However, detection can be difficult, and it also can be difficult to diminish the off‑farm sources of stray voltage coming into the farm.
Sources within the farm often can be corrected if they are discovered. Again, it also is difficult to find the source of the stray voltage within a farm, as it is possible for a single motor to be going bad and throw much stray voltage, even though it has not completely failed yet. Because stray voltage often occurs only intermittently on a farm, it often goes unnoticed. With the installation of the monitoring equipment on this farm, sources of stray voltage are detected much quicker and can be localized easier.