Background and history

Back muscle necrosis is part of the porcine stress syndrome (PSS) and in affected pigs degenerative changes take place in the back muscles along each side of the spine. It is usually seen in the young growing gilt although occasionally it occurs in the adult female.

The condition sometimes occurs in outdoor gilts that have heavy ham muscles, when they are moved into paddocks for the first time. Within five minutes or so a number of the gilts can be very stiff and lame.

The condition can take two or three weeks to resolve and the breeding capacity of the gilts may be affected. The disease is relatively uncommon.

Similar diseases include: acute erysipelas; fractures; mycoplasma arthritis; leg weakness (OCD); spinal damage.

Clinical signs

• The signs are sudden in onset after exercise.
• Severe pain in the lumber muscles with obvious swellings.
• Incoordination.
• Death (necrosis) of muscle fibres with haemorrhages into the tissues themselves.
• Lameness – reluctance to stand.
• Adopt a dog sitting position.
• The temperature is usually normal but may be elevated.
• Discoloration of the skin over the affected area.

Diagnosis

Based on the clinical signs. The pig can be made to stand with difficulty but there is no evidence of fractures. Examine the lumber muscles carefully, they will be swollen and painful on pressure. History includes sudden lameness associated with movement and acute pain.

The temperature is usually normal but may be elevated.

Causes

• Sudden movement, e.g. from confinement to outdoor accommodation.
• Presence of the halothane gene.

Prevention

Breed from pigs that are free of the stress gene.

Treatment

• Inject with phenylbutazone 1ml/50kg or other pain killer.
• Inject with corticosteroids provided the animal is not pregnant.
• If there is a temperature give an injection of long-acting penicillin to cover the possibility of erysipelas.