Infectious stunting syndrome associated with disturbances of mineral metabolism and bone development in broiler chickens

On a broiler farm with a rearing capacity of about 200,000 chickens, a dise ase characterised by growth retardation, variability in chick size, 'leg we akness', diarrhoea and increased mortality at 3 weeks of age occurred repea tedly, in several successive broiler flocks. Gross and histopathological fi ndings were dominated by widening of the hypertrophic and ossification laye rs of the physes of long bones as well as by thickening, unevenness and def ective calcification of the cartilage trabeculae. In the parathyroid gland, vacuolar degeneration of the cytoplasm of glandular epithelial cells, conn ective tissue proliferation and, here and there, cyst formation were seen. Additional findings included severe cerebellar oedema and neuronal degenera tion. The pancreatic, myocardial and intestinal changes typical of infectio us stunting syndrome (ISS) occurred only in a mild form. Four-week-old chic kens exhibiting 'leg weakness' had significantly lower blood inorganic phos phate concentration and tibial ash content as compared to healthy chickens. The disease was successfully transmitted by oral administration of small i ntestinal homogenate from affected chickens. In a second experiment, howeve r, the disease could not be transmitted with intestinal homogenate steriliz ed by irradiation. Large doses of vitamin D-3 reduced the rate of growth re tardation and defective calcification of bones. The digestive enzyme activi ties of the pancreas and small intestinal mucosa of 'infected' chickens wer e decreased as is typical of ISS.