الفهرس 
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Abstract
The present study performed in two experiments. The first one applied to study the effect of Mycoplasma gallisepticum (MG) infection on antibodies titer of inactivated viral vaccines evaluated in SPF chickens. The results achieved by vaccination of 20 groups of chicks (25 chicks per group) with ND (Newcastle disease), AI (Avian Influenza), IB (Infectious Bronchitis), IBD (infectious bursal disease) and Reo inactivated viral poultry vaccines. For each vaccine group of chicks was experimentally pre-infected with MG strain then vaccinated, group was infected with MG strain and simultaneously vaccinated, in addition to a group was infected with MG strain 5 days after vaccination, while the last group was only vaccinated. The experiment revealed that all pre- infected groups showed highest antibody titer against ND, AI, IB, IBD and Reo (7.4 Log 2, 7.1 Log 2, 20EU, 20 EU and 17 EU, respectively) at 28 days old post vaccination. The lowest titer was appeared in non infected vaccinated groups with ND, AI, IB, IBD and Reo (6.5 log2, 6.5 log2, 12EU, 14 EU and11EU, respectively).
The second one applied to understand not only the disease process caused by Mycoplasma gallisepticum (MG) but also to understand the interference with evaluation of some live attenuated poultry viral vaccines. The study carried out to investigate the titration and potency of some live attenuated poultry viral vaccines: ND (Newcastle disease),IB( Infectious Bronchitis) , IBD (infectious bursal disease) and Reo in both SPF Embryonated chicken eggs (ECE) and chickens which revealed that the highest titer of these vaccines were appeared in MG pre contaminated ECE were 1011, 107.5,107.9 and 107.5, respectively and the lowest vaccine titters were appeared in non MG contaminated Embryonated chicken eggs were 108, 106 , 106.8, and 106, respectively. While the potency of these previous vaccines indicated that the highest antibodies titer were appeared in MG pre infected vaccinated chickens were 7.5 log2, 36EU, 42 EU and 14 EU, respectively and the lowest antibodies titer were appeared in non MG infected vaccinated chickens were 6.5 log2, 12 EU, 17 EU and 10 EU, respectively. Our findings underline the importance of using Mycoplasma-free eggs or chicken for the production and evaluation of viral vaccines.