Background and history

This term covers a group of conditions associated with an autosomal recessive gene. It includes acute stress and sudden death (malignant hypothermia), pale soft exudative muscle(PSE), dark firm dry meat, and back muscle necrosis. Heavy muscle pigs are more likely to carry the gene. The pig is either homozygous recessive (susceptible) heterozygous, or free of the gene.

The gene can be identified by the pigs response to the anaesthetic gas halothane but recent developments have produced gene probes using blood, that identify both the homozygous and heterozygous carriers.

Similar diseases

These include the other causes of sudden death, twisted bowel, internal haemorrhage, mulberry heart disease and pyelonephritis. Hypocalcaemia in the lactating sow although uncommon can give identical symptoms to PSS.

Clinical signs

Piglets

• Rarely seen.
• If so as in sows.

Sows

The onset is sudden with:-

• Marked muscle tremors.
• Twitching of the face.
• Rapid respiration.
• The skin becomes red and blotched.
• Death usually occurs within 15-20 minutes.
• Rigor mortis (stiffening of the muscles after death) within 5 minutes is a striking feature.
• Rise in temperature > 41 degrees C (106 degrees F).

Weaners and growers

• The onset is sudden with muscle tremors.
• Twitching of the face.
• Rapid respiration.
• The skin becomes red and blotched.
• Death usually occurs within 15-20 minutes.
• Back muscle necrosis is a more localised form of PSS.
• Whilst the gene produces a leaner carcass, growth rates are slower and the levels of sudden death increase.

Diagnosis

This is based on the sudden onset, symptoms, breed, susceptibility and the known presence or absence of the gene in the pig. In many cases the pig is just found dead and a post-mortem examination is necessary to eliminate other disease. Rigor mortis (stiffening of the muscles after death) within 5 minutes is a striking feature.

This condition has to be differentiated from other causes of sudden death, twisted bowel, internal haemorrhage, mulberry heart disease and pyelonephritis.

Causes

• Disease is precipitated by sudden muscle activity.
• The carrier pig is genetically susceptible.

Prevention

• Remove the gene from the population.
• Use a homozygous or heterozygous male on stress gene free females if the gene is to be used to improve carcase quality.
• Maintain a gene free herd.

Treatment

This is usually ineffective but the following are worth adopting:

• Spray the pig with cold water to control the temperature rises.
• Inject 50-100ml of calcium gluconate (used in cows for milk fever) by intramuscular injections at two separate sites. Seek veterinary advice.
• Sedate the pig with stresnil.
• Do not move or cause undue muscle activity.
• Give an injection of vitamin E 2iu/kg.