Occurrence: Worldwide. Species affected: All. Age affected: Young.

Causes: Failure of the chondrocytes to hypertrophy (increase in size) results in abnormal cartilage, which cannot be invaded by blood vessels. The disease is not contagious. Genetic and/or dietary (caution-anion ration or high phosphorus relative to calcium) factors may be involved. Grain high in Fusarium roseum or fungicide (tetramethylthiuram) can cause the disease.

Effects: Bowing of the bones is evident, which is more severe in roaster birds or males kept over 8 weeks for de-boning with body weight over 2.2kg (5lb). Lameness can occur in as many as 30% of the flock, so reluctance to move, stilted gait and bilateral swelling of the femoral;-tibial joints can be seen.

All species of young bird are susceptible to this chronic disease. The aetiology of the disease is the failure of the chondrocytes to hypertrophy (increase in size) resulting in abnormal cartilage, which cannot be invaded by blood vessels. Vascular invasion of the cartilage from the metaphysis is not adequate and/or defective chondrolysis occurs.

This disease is not contagious. Genetic and/or dietary (caution – anion ratio or high phosphorus relative to calcium) factors may be involved.

Grain high in Fusarium roseum or fungicide (tetramethyl thiuram sulphate) can cause the disease.

Lameness can be seen in as many of 30% of the flock (reluctance to move, a stilted gait and bilateral swelling of the femoral-tibial joints).

Bowing of the bones is evident and is more sever in roaster birds or males kept over 8 weeks for de-boning with body weight over 5 lbs or 2.2 kg.

Proximal tibiotarsal bone is enlarged and contains an abnormal mass of cartilage (failure of cartilage in growth plate to become calcified).

Fractures below the abnormal cartilage may occur.

History, clinical signs and postmortem lesions (abnormal mass of cartilage in tibial head) are characteristic. Microscopically, dyschondroplasia is characterised by persistence and accumulation of pre-hypertrophic cartilage and begins as early as the first week of age. Chondrocytes in abnormal cartilage are smaller and shrunken.

It simulates perosis, rickets and osteochondrosis (necrosis of growth plate primarily in the vertebrae and femoral head).

Lyxoscope can detect TD in birds as young as one week of age. This machine is used by basic breeder companies to select out TD in their genetic lines.

Slow the growth rate and select strains with a lower incidence of TD.

Diet changes, such as reducing phosphorus relative to the level of calcium, will reduce the disease. Feed a diet free of Fusarium and tetramethyl thiurams sulphate.

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