SUMMARY. Septicemia-Toxemia (sep/tox) is under the United States Department of Agriculture (USDA) food safety category -1 and is the most common and economically significant cause of broiler carcass condemnations. Hepatic lesions are considered a possible consequence of septicemia and associated bacterial contamination of the carcass. Thus, these lesions are considered an indicator of sep/tox (sep/tox hepatitis). This study was undertaken to analyze the histologic lesions preceding grossly visible liver lesions leading to condemnation due to sep/tox at the processing plant. Livers from carcasses of broilers condemned by USDA inspectors for sep/tox were used to establish microscopic and gross criteria of end-stage sep/tox hepatitis. Following the characterization of sep/tox hepatitis, broilers from a farm with a history of sep/tox condemnations were submitted for necropsy and bacteriological investigation at four intervals during the final 20 days of production. Five healthy and five clinically ill chickens were submitted from four houses at 18, 25, 32 and 38 days of production (160 total). Microscopic lesions representing in hepatic perisinusoidal myofibroblast proliferation (HPMP), periportal extramedullary granulopoiesis (PEMG), splenic follicular histocytosis (SFH), and bone marrow cellularity (BMC) were graded subjectively for each bird and subjective grading was evaluated with digital quantitative techniques. Peri-sinusoidal hepatic stellate cells (HSC) morphology and progressive transformation of these cells into myofibroblasts was confirmed by immunohistochemistry for smooth muscle actin and desmin. Aerobic cultures of livers and gall bladders from sep/tox birds yielded no growth of bacteria associated with septicemia. Mild to severe HPMP was observed in all age groups representing 28% of examined birds. Increases in inflammatory cells observed by PEMG and BMC were positively correlated with progressive HPMP and end-stage sep/tox hepatitis in broiler chickens.

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