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 disease characterised by growth retardation, variability in chick size, 'leg weakness', diarrhoea and increased mortality at 3 weeks of age occurred repeatedly, in several successive broiler flocks. Gross and histopathological findings were dominated by widening of the hypertrophic and ossification layers of the physes of long bones as well as by thickening, unevenness and defective calcification of the cartilage trabeculae. In the parathyroid gland, vacuolar degeneration of the cytoplasm of glandular epithelial cells, connective tissue proliferation and, here and there, cyst formation were seen. Additional findings included severe cerebellar oedema and neuronal degeneration. The pancreatic, myocardial and intestinal changes typical of infectious stunting syndrome (ISS) occurred only in a mild form. Four-week-old chickens exhibiting 'leg weakness' had significantly lower blood inorganic phosphate concentration and tibial ash content as compared to healthy chickens. The disease was successfully transmitted by oral administration of small intestinal homogenate from affected chickens. In a second experiment, however, the disease could not be transmitted with intestinal homogenate sterilized by irradiation. Large doses of vitamin D3reduced the rate of growth retardation and defective calcification of bones. The digestive enzyme activities of the pancreas and small intestinal mucosa of 'infected' chickens were decreased as is typical of ISS