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Leg Weakness

"Leg weakness" is an imprecise term used to describe different forms of lameness. For example, it is sometimes used to describe poor leg conformation. More often it is used to describe a clinical condition associated with degeneration of the bone and cartilage, called osteochondrosis (OCD).

Changes in the cartilage that lead to clinical OCD take place in most modern pigs from as early as two months of age. The severity and its effect depend largely on the environment and the speed of growth of the animal. OCD in modern pigs results from the many years of selecting animals for rapid growth, large muscle mass, and efficient feed conversion and therefore much greater weight on the growth plates whilst they are still immature, together with the stresses of intensive methods of production.

OCD may be seen within three months of gilts being introduced on to the farm, during their first pregnancy, in lactation or in the first 2 to 3 weeks post weaning.

Leg deformities are common in the rapidly growing pig but are usually of no commercial consequence. Separation of the head of the femur at the growth plate however occurs in rapidly growing pigs on some farms.


  • None.

In acute cases of OCD:
  • There is separation of the bones at the growth plate resulting from sudden movement.
  • The animal walks on three legs, the affected leg swinging freely.
  • Crepitus, the rubbing of the broken bones together, can usually be felt.
  • Fractures in the spine can also occur particularly during lactation and immediately post weaning.
  • In such cases the sow is in acute pain.
  • Often in a dog sitting position with the hind legs well forward.
  • Nervous signs.
In chronic cases of OCD, the onset is gradual.
  • The sow shows abnormal leg conformation and gait with or without stiffness and pain.
  • The temperature and affected joints remain normal.
  • The front legs may be straight, the pig walking with a long step on its toes, or the knees may be bent inwards or flexed, the pig walking with short steps. In some old sows, the pasterns may be dropped. The feet may be rotated or twisted.
  • The hind legs are often straight, the pig walking with a swinging action from the hips. In some cases the legs are tucked beneath the body. The hocks are turned inwards and are close together. The pig walks with a goose stepping action. Again in old sows the pasterns may be dropped.
Weaners & Growers
  • Acute cases are characterised by the sudden onset of acute lameness, highlighted by poor conformation of legs, bending of bones and dropped pasterns.
  • The pig refuses to put the foot to the floor.
  • Fractures in the hip, knee and shoulder joints. Evident at slaughter or post mortem.
  • Long-term the joint changes may lead to arthritis.

Causes / Contributing factors

  • Environmental factors that cause the foot to slip on the floor.
  • The design of slats can contribute to OCD. Some slats slope to the edges from the centre and are so smooth that when the animals stand, the feet slip into the gaps, causing repeated pressure on the growth plates.
  • Full confinement of pregnant gilts when they are still growing can be a major contributing factor.
  • Are the gilts mixed with sows at weaning? The modern hybrid gilt often suckles produces large litters and large amounts of milk which depletes her body calcium and phosphorous. The bones become weak and are therefore more prone to injury.
  • High levels of vitamin A (in excess of 20,000 iu/kg) particularly in the younger growing pigs can interfere with the normal development of the growth plates.
  • High stocking densities increase the incidence, particularly in the growing period and where animals are housed on solid concrete floors or slats.
  • Trauma.
  • Rapid weight gain.


This is based on the clinical signs. There are no laboratory tests and post-mortem examinations may be misleading because many pigs that were not lame before death may be found to have lesions.

OCD has to be distinguished from Mycoplasma hyosynoviae and erysipelas arthritis.

Further Reading

Click on the links below to find out more about this disease, including treatment, management control and prevention information. The top link is the main article on this disease.