Infectious stunting and leg weakness in broilers: I. Pathology and biochemical changes in blood plasma

A syndrome of stunting and leg weakness could be reproduced experimentally by inoculation of 1-day-old broilers with homogenised intestines from affected birds. Inoculated birds kept in isolators showed highly impaired growth until 3 weeks p.i. Birds produced mucoid yellowish coloured droppings and at post mortem thin liquid intestinal contents were found. Biochemical examination of blood plasma showed low plasma carotenoid concentrations and an increased alkaline phosphatase (ALP) activity, mainly caused by one isoenzyme, which was most likely of intestinal origin. These findings implicate infectious causal agents with the intestines as the site of primary involvement. Bone abnormalities consisted of rickets-like changes at the age of 3 weeks, whereas a distinct dyschondroplasia was seen at 4 weeks. The syndrome could also be transmitted to uninoculated birds kept in contact with birds inoculated at 1 day of age. Birds inoculated at 7 days of age also showed greatly impaired growth but developed no macroscopical bone disorders. Inoculation at 14 days of age did not result in impaired growth or bone abnormalities. Following inoculation with REO virus, isolated from a field case, no bone abnormalities occurred. However, a shortlived impaired growth, diarrhoea, increased plasma ALP activity and decreased carotenoid concentration were observed. The rapid spread of the disease and the role of REO virus are discussed.