The Duchess Fund recently has received medical reports on two purebred potbellied pigs from registered stock involving Porcine Stress Syndrome (PSS). PSS is also known as “Malignant Hyperthermia”.
CASE A – CONFIRMED (Case #000196 – Duchess Fund Medical Database) The first case was in July, 2000 when a pig expired on the table at a university during a routine spay. PSS was suspected so a cardiac puncture was done and blood sent off for DNA testing. The result of the DNA test was homozygous, HAL 1843 dm, which means she was a dimutant or had two copies of the mutant PSS gene and malignant hyperthermia (same as PSS) was the cause of death. A complete summary will be in Part II.
CASE B – SUSPECT (Case #000197 – Duchess Fund Medical Database) The second case was on a young piglet with a history of being easily stressed. It was reported that she had a difficult recovery following her spay. The pig expired approximately 3 months after the spay. The owners took the pig to a university for a necropsy. We have the pathology report as well as the liver tissue analysis. There was no selenium deficiency. Fresh blood was not available for DNA testing because the pig had expired hours before reaching the university. However, based on the history of the pig, microscopic change in muscle tissue and the selenium tissue analysis of the liver, the parents are being DNA tested for PSS. Test results will be in Part II as well as a complete summary.
Naturally, this has raised many questions from concerned pet pig owners. In an effort to better explain this genetic syndrome, we asked Barbara Straw, DVM, PhD, to share her expertise on the subject for the benefit of potbellied pig owners. Dr. Straw is the Editor-In-Chief of “Diseases of Swine” 8th edition.
The following is an interview on 9/21/00 conducted by The Duchess Fund:
Duchess Fund: Dr. Straw, could you explain in layman’s language what Porcine Stress Syndrome is (also known as malignant hyperthermia) ?
Dr. Straw: Porcine Stress Syndrome (PSS for short) is an inherited defect in muscle metabolism that can be life-threatening to the pig under certain triggering situations. Pigs with PSS have a defect in the transport channel that moves calcium into their muscle cells. Normally for a muscle to contract, calcium must be moved from outside the cell to inside. In certain situations, this defect in which the muscle is trying to function without the right level of calcium results in abnormal muscle metabolism in which lactic acid builds up. Accompanying the acidosis is a build-up of heat due to a wasteful process of utilizing muscle glycogen for energy. The acidosis and hyperthermia can be severe enough to cause death. PSS is caused by a recessive gene. When animals carry two copies of the gene they are prone to showing clinical signs when certain stresses are applied.
Duchess Fund: What is the difference between PSS and White Muscle Disease?
Dr. Straw: White Muscle disease occurs because of a deficiency of an essential nutrient, selenium. Selenium is part of an enzyme that removes peroxidase waste products from liver, muscle and many other cells in the body When peroxidases accumulate in muscle they damage the tissue and it blanches out producing a “white muscle”. While both PSS and selenium deficiency produce damage to muscle, they have completely different causes.
Duchess Fund: Since PSS is a genetic disease, could a supplement of Vitamin E and/or Selenium or any other vitamin/mineral supplement prevent symptoms or prevent death from PSS?
Dr. Straw: No. PSS is a genetic disorder not a nutritional deficiency and the nutritional status of a pig has not been shown to affect the expression of PSS. Supplementation with selenium or Vitamin E would not influence the expression of PSS since they are caused by two separate mechanisms. Calcium supplementation would not help either since there is plenty of calcium outside the muscle cell, but the cellular transport channel isn’t working properly.
Duchess Fund: Under what conditions are pigs with PSS likely to show symptoms and possibly die?
Dr. Straw: Transportation, high environmental temperatures, exercise, mating and fighting can trigger muscle damage. Also certain compounds such as halothane anesthetic, succinylcholine and caffeine directly act on the calcium transport channel.
Duchess Fund: What is Dantrolene, how and when is it used and how effective is it?
Dr. Straw: Dantrolene is a drug given by injection that acts to stabilize the calcium transport channel. It has moderate to high effectiveness in treating an episode of PSS if given immediately after signs are noticed. However, because PSS is not a common condition, few veterinary clinics stock this drug.
Duchess Fund: Can a pig have a non-fatal PSS episode without spiking a high temperature?
Dr. Straw: An elevation in temperature is a consistent finding with PSS. The abnormal muscle metabolism generates excess heat that raises the rectal temperature. Events such as exercise or fighting that trigger an episode of PSS may also raise the pig’s temperature. While an elevation in temperature by itself is not diagnostic, a pig with a normal temperature subjected to such events, is not likely to be experiencing a PSS episode.
Duchess Fund: If a veterinarian treats a pig that subsequently dies, what should that veterinarian do to confirm PSS if it was suspected?
Dr. Straw: When a pig dies after stressful physical activity or anesthesia, the first thing to do is take its temperature. PSS produces extreme elevations in body temperature, typically as high as 106 degrees F at the time of death. Even some time after death the muscle temperature will still be elevated. Next check for extreme rigidity of the legs. The abnormal events in the muscle produce immediate rigor mortis. The definitive test is to directly check for the defective gene, called HAL-1843. This test requires a sample of blood or tissue to be sent to a lab that performs DNA analysis. The laboratory will report whether the pig has two, one, or no copies of the HAL-1843 gene.
Dr. Barbara Straw, DVM, PhD
Professor Swine Medicine
Michigan State University
END OF INTERVIEW
We appreciate Dr. Straw taking the time to address this issue and thank her
for her assistance!
As you can see, PSS is an inherited defect in muscle metabolism. Dr. Straw has outlined the causes and symptoms of this syndrome as well as the steps that should be taken to diagnose and confirm it.
At this time it is unknown if Case A is an isolated case or if there are more potbellied pigs carrying the gene. As for Case B, the DNA test results on the pigs’ parents will determine whether or not PSS was involved in the cause of death. Many swine experts believe that PSS is a minimal problem in potbellied pigs. We need more information and monitoring to confirm this.
If you are interested in having your pig tested for PSS, the following needs to be done:
Contact: Ed Kenney at Swinetics, phone 877-440-0894 who will register you free of charge.
After registration with Swinetics, contact Jarrod Watson at GeneScreen, phone 800-752-2774 and he will send you the material for the card test which consists of a few drops of your pigs blood placed on a card and mailed to their lab. Registration with Swinetics first will reduce the cost of this test. Please furnish a copy of the test results to your veterinarian and The Duchess Fund so we can document it.
In Part II of PSS, we will be covering stress reducing management practices, alternative methods of medical management of pigs as well as the summaries of these cases.