The present work aimed to investigate the histopathological aspects, growth performance, urea residue in muscle and liver of broiler birds and chemical composition of the breast muscles in birds fed graded levels of urea -treated ration. 80, day old chicks were reared for 6 weeks. After one week of age, chicks were randomly divided into 4 equal groups fed on 1.25%, 2.5%, 5% and 0% urea in their ration. Five birds from each group were sacrificed at the day 7, 14, 28 and 35 from adding urea. The most clinical signs were respiratory symptoms, watery diarrhea and staggering gait. Body weight and feed consumption were increased in group I & II, while the group III showed mild decrease. Urea residue in muscle and liver increased significantly in group III when comparing with other groups. The chemical composition of the muscle showed that the moisture content in group III was high than group IV. There was non-significant increase in the crude protein level in group II. There was significant increase in ash percent in group II. The fat content in the muscle of all urea treated groups was significant decrease than IV group. Grossly, kidneys and the liver were severe enlarged with pale anemic and mottled coloration. Lungs and the muscles were severe congested and dark brownish color with petechial and linear hemorrhage in muscle. The brain showed mild hyperemia. Histopathological examination in the kidneys showed degenerative changes in the epithelial cell lining of the renal tubules. The glomeruli showed shrinkages of their glomerular tuft and hyalinization of the Bowman's capsules. Liver showed focal areas of necrosis in the hepatic parenchyma. There was severe thickening of the hepatic capsule. The bile duct showed hyperplasia of their epithelial cell lining with the presence of desquamated epithelia in the ductile lumen with newly formed bile ductile. Most of hepatic and pulmonary blood vessels showed thrombosis. Lungs and muscle and brain showed congestion of the blood vessels. The bronchioles showed catarrhal bronchopneumonia. There was osseous metaplasia among the pulmonary tissue. The neuron was suffering from Tygrloysis with presence of satellotosis and neurophagia. The intestine showed degenerative changes. Myomalecia of some muscle cell and suffering from mild degree of hyaline degeneration. It is recommended that lower inclusion levels of urea diets (1.25%) rather than the 2.5% and 5% used in this study be employed for a short period of time.
