ThePigSite Pig Health
Leg Weakness (Osteochondrosis - OCD)
(270) Trauma is by far the most common cause of lameness in the dry sow from point of weaning to point of farrowing. Environmental trauma to the coronary band area and to the sole or wall of the foot results in penetration of the sensitive tissues, infection and lameness. These foot conditions are called bush foot and foot rot. Trauma however, more commonly arises indirectly from other causes within the environment that create shear forces on the muscles, tendons, bones and bone structures. Such changes associated with cartilaginous structures are referred to as leg weakness or osteochondrosis. The structure of the joint and bone is shown in Fig.7-7.
The term Leg weakness" is also used sometimes to describe poor leg conformation or describe a clinical condition associated with lameness and stiffness. It arises due to abnormal changes in the articular cartilage and the growth (epiphyseal) plates. These plates are responsible for the growth of bones both in length and diameter. Whilst the exact mechanisms that cause these changes are not fully understood they arise due to the pressure and shear stresses that are placed upon these rapidly growing tissues. This pressure reduces the oxygen supply, causing abnormal growth and consistency of the cartilage. Damage to the cartilage tends to be progressive and irreversible. The damaged cartilage is replaced by fibrous tissue. This cartilage damage in turn produces shortening and bending of the bones near the joints and at the extremities of the long bones. Weak epiphyseal plates also have a tendency to fracture and cartilage covering the joint surfaces splits and forms fissures. It is important to appreciate that such changes in the cartilage take place in most if not all modern pigs from as early as two months of age. In some cases many of these can only be detected under the microscope. It is interesting to note that such changes can not be detected in the wild boar which takes up to two years to reach maturity. OCD is therefore a fact of life in modern pig production but its severity and its effects depend largely on the environment. OCD 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. Conversion of cartilage to bone involves the deposition of calcium and phosphorous and while the process of breaking down and reforming bone goes on throughout life, bone growth ceases when the sow is approximately 14 to 16 months of age.
It is not uncommon in breeding enterprises for 20 to 30% of boars and gilts to be culled after completing the performance test, due to leg weakness and leg deformities.
The conformation of the pig is a predisposing factor to OCD, Fig.7- 8 shows some of these traits.
Sows with good leg conformation show angulation of the bones at the hip, knee and hock joints. The bones below the hock slope slightly forwards and the feet are well placed on the ground. Sows that are susceptible to leg weakness are straight legged with little angulation of the bones between the joints and the back tends to be arched. This alignment increases shear stresses on the growth plates.
Clinical signs
Acute disease
Chronic disease
Front legs
Diagnosis
OCD is diagnosed on the clinical signs described. There are no serological or other tests and post-mortem examinations may be misleading because many pigs that are found to have joint lesions may not be lame.
Similar diseases
There are two, Mycoplasma hyosynoviae infection and erysipelas. In both of these the disease is usually sudden in onset sometimes with a raised body temperature and there is pain and swelling in the joints. A differentiating feature is the response to treatment. OCD does not respond to antibiotics whereas Mycoplasma hyosynoviae and erysipelas will respond within 24 to 36 hours, the former to lincomycin or tiamulin and the latter to penicillin.
Treatment
If OCD is causing a problem on your farm check through the list below and identify those points that are important in your system.
This is seen when there is a separation or fracture of the bones at the epiphyseal plate (epiphyseolysis) associated with sudden movement. The animal walks on three legs, the affected leg swinging freely. Crepitus or rubbing of the broken bones together can usually be felt. Sudden fractures can also occur in the knee and elbow joints, which are more common in the young growing pig. Fractures of the vertebrae in the spine 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. Animals housed in farrowing crates with slippery floors tend to slide the back legs forward and there is a risk of the hind muscles pulling away from their attachments to the pelvis (apophyseolysis). In such cases the sow will stand with assistance but it cannot pull the hind leg backwards. When it is placed on to the ground it just slides forward. Such animals should be culled immediately.
The onset is gradual. The pig shows abnormal leg conformation and gait with or without stiffness and pain. The temperature remains normal and joints will not be swollen unless there are fractures.
Hind legs
Abnormal gaits arise either from pain in the joints or abnormal movements in the hind legs from the hips which give a swaying motion. The pain is associated with damage to the sensitive membranes around the joints resulting from either splitting or erosion of the cartilage in the joints or movement of the growth plates. Some pigs however may show severe clinical signs yet on post mortem examinations the joints appear normal and vice versa. Joints may become inflamed (arthritis), particularly in the hip, knee and elbow. 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.
Management control and prevention
