Sivaseelan, SBalasubramaniam, GABalachandran, PMadheswaran, RTANUVAS2020-06-162020-06-162014-01http://krishikosh.egranth.ac.in/handle/1/5810147643TNV_SIJVS_2014_1(3)27-32Pathobiology of uncomplicated Ornithobacterium rhinotracheale (ORT) infection in layer chicken was evaluated in 30 commercial layer chicken farms. Ornithobacterium rhinotracheale organism was confirmed by its growth characteristics on agar media and typical morphology on Gram’s staining. Commonly encountered concurrent respiratory virus and bacteria were ruled out. Polymerase chain reaction technique was used to rule out Mycoplasma gallisepticum. Newcastle disease and Infectious bronchitis were screened by haemaggutination and inhibition tests and bacterial diseases like Colibacillosis, Pasteurellosis and Infectious coryza were ruled out by culture and staining techniques. Uncomplicated cases of ORT revealed mild sinusitis with crusts in the external nares, mild subcutaneous swelling of face, catarrhal rhinitis and tracheitis, airsacculitis and unilateral or bilateral pneumonic changes of the lungs. Foamy, whitish, yogurt like exudates with strands of fibrin was observed in the abdominal airsacs. Gross and histopathological changes were observed throughout the respiratory tract and seven per cent mortality was recorded in the uncomplicated cases.enVeterinary ScienceArticle