Porcine stress syndrome, sometimes called malignant hyperthermia or transport myopathy, is a complex, genetically transmitted myopathy usually triggered by stress or excitement. It also can be triggered by several anesthetics, including halothane, and by depolarizing muscle relaxants. Signs that appear can include tremors of the tail, back or leg muscles, muscle rigidity, inability to walk, respiratory distress, hyperthermia, blotchy dermal hyperemia, acute right heart failure, and death. Savaging of neonatal piglets by PSS-positive dams has been reported.
Postmortem lesions include early, rapid and complete rigor mortis, pulmonary edema and pale soft musculature often containing hemorrhages. Carcasses of slaughtered swine with PSS are blanched, wet and may drip excessive amounts of fluid. The meat is referred to as pale, soft, exudative (PSE) pork. Shoppers discriminate against it in the market place.
The basic abnormality is an inherited defect in the mechanism for uptake, storage and release of calcium in muscle fibers. Efforts to eliminate PSS through genetic selection have led to success in identification and elimination of a stress gene in many genetic lines but this trait is also linked to heavily muscled phenotype. A polymerase chain reaction test is widely available and used to identify hetero- and homozygous carriers of the halothane gene; both types of carrier animals should be culled.