الفهرس 
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Abstract
Four experiments were designed for detection of the effect of E. coli serotype 078 and serotype 0166 by different routes on the severity of Salmonella enteritidis, Mycoplasma gallisepticum and lBD V in broilers, and the obtained results were: In experiment 1, broiler chicks were infected at 21 th day with K,coli 078 and 0 166 infections in different routes (LM and LT). There was a significant difference in mortality rate, clinical signs, lesions and performance index according to the route of infection: 1- The mortality rate was 10 and 20% in groups 1 and 2 (LM) respectively and decreased performance index. 2- The mortality was 20 and 30% in groups 12 and 13(I.T) respectively but the decrease in performance index was more clear than groups 1 and 2. 3- Birds in all infected groups showed general signs of illness. Moreover, all infected groups showed respiratory signs 20-70% and 40- 100%, diarrhea 30-90% and 20-50%, conjunctivitis 0-30% and 0-50% in groups infected LM and LT respectively. 4- Histopathological examination for all group showed lesions in heart and lungs. In experiment 2, broiler chicks were infected at 21 th day with E.coli 078 and 0166 by different routes LM and LT with Salmonella enteritidis orally. There was a significant difference in mortality rate, clinical signs, lesions and performance index between mixed infections and single infection: 1- There was no morality in single infection but decreased performance index. 2- The mortality rate was 10-20% in mixed infections but the decrease in performance index was more clear than in single infection.