الفهرس 
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Abstract
The study was conducted at Department of Bacteriology, Mycology and Immunology, Faculty of Veterinary Medicine, University of Sadat City. This study aimed to investigate the effect of feed additives as probiotics (Protexin) and probiotic products ( Nutrilac, I. G. A) on the immune response and growth performance parameters in broiler chickens. A total of 300 broiler chicks (Arbor Acres) were assigned into 15 groups (20 each), the experiment was continued for five weeks (35 days), The 1st group is a control group received the basal diet only without vaccine or challenge. The 2nd group is a control group received the basal diet and vaccinated 0.5 ml of mixed multi-strain vaccine of E.coli O78, O26, Salmonella Enteritidis, and Salmonella Typhimurium with at the 1st day then challenged with E.coli O78 live mixture of same vaccine strains at the 8th day. The 3rd group is control group vaccinated 0.5 ml at 8 day then challenged with E.coli O78 at the 16th day. The 4th group received probiotic (Protexin) and challenged at day 8 with no vaccine. The 5th group received probiotic products ( Nutrilac, I. G. A). As a commercial probiotic product in a dose of 3 ml / Liter during first 1-5 days with no vaccine. The 6th group received Protexin and Nutrilac, I. G. A and challenged at day 8. The 7th group vaccinated with a dose 0.2 ml s/c at the 1st day and challenged at day 8th.The 8th group vaccinated with a dose 0.5 ml at 8th day and challenged at the 16th day. The 9th group received only Protexin and vaccinated with a dose 0.2 ml s/c at the 1st day and challenged at the 8th day.The 10th group received only Protexin and vaccinated with a dose of 0.5 ml at the 8th day and challenged at the 16th day. The 11th group received Nutrilac, I. G. A as a probiotic product and vaccinated with a dose of 0.2 ml s/c at the 1st day then challenged at the 8th day . The 12th group received only Nutrilac, I. G. A and vaccinated with a dose of 0.5 ml at the 8th day then challenged with at the 16th day. The 13th group received Protexin and Nutrilac, I. G. A and vaccinated with a dose of 0.2 ml s/c at the 1st day then challenged at the 8th day. The 14th group received Protexin and Nutrilac, I. G. A and vaccinated with a dose of 0.5 ml at 8 day and challenged at the 16th day. The results were compared with the control groups and recorded as follows that: the immune response to Salmonella Typhimurium, Salmonella Enteritidis, E.coli O78 and E.coli O26 at the 7th day showed that G4, 5, 6, 7, 9, 11, and 13 gave the highest results and at the immune response at the age of12 days the groups G4, 4, 11, and 13 provided the highest results while at the day 15 the groups G4, 5, 6, 7, 11 and 13 gave the highest results and overpassed the results of the previous age. While the immune response to Salmonella Typhimurium, Salmonella Enteritidis at the day 15, 20 and 25, the groups G8, 10, 12, and 14 produced the highest results .While the response to E. coli O26 and E.coil O78 at the age of 15 days, 20 and 25, the groups G8, 10, 12, and 14 provided the highest results. The result of a total mortalities, the groups G1, G2, and G8 expressed high mortalities compared with other groups on the contrary to that the G11 showed zero mortality. While the results of cytokines (It was noticeable that the measured cytokines (IL12, IL4, IFN-γ) in the vaccinated groups, administered probiotic or administered probiotic product, or simultaneous administration of vaccine, probiotic, and probiotic product in different regimes was lower than the negative and the positive control groups. showed that probiotic could be modulate the immune response to Salmonella Typhimurium, Salmonella Enteritidis, E.coli O78 and E.coli O26 usually act directly by increasing the activity of macrophages, modulating the secretion of immunoglobulins or cytokines, or indirectly by enhancing the gut epithelial barrier and altering the mucus secretion. Meanwhile, the addition of probiotic or the probiotic product, either singly or in combination with vaccination regimen 0.2 ml at the first day of age lowered the mortalities at the beginning of rearing age and after challenge with a mixed culture of E.coli O26, E.coli O78, Salmonella Enteritidis, and Salmonella Typhimurium. It was noticeable that the measured cytokines in the vaccinated groups, or administered probiotic or administered probiotic product, or simultaneous administration of vaccine, probiotic, and probiotic product in different regimes was lower than the negative and the positive control groups. It was clear that the supplementation of probiotic and probiotic product either singly or being combined with vaccination 0.2 ml at the beginning of rearing age improved the haematological parameters, PCV, Hb and RBCs. Also these compounds increase the total leukocyte and lymphocyte counts of groups when being administered with the combined vaccine which was administered with different regimens . The data represented the results of haemoglobin, packed cell volume (PCV), RBCs and WBCs count at the age of 7 days proved that the highest groups were 6, 5,7,9 and 11. While at the age of 12 days evidenced that the highest results were from G4, 5, 7, 9, 11 and 13. Furthermore, at the age of 12 days all the groups 4, 5, 6,9,11 and 13 gave the highest results. At the age of 20 days, the groups G8, 12 and 14 gave the highest results. While at the age of 25 days, the groups G1, 8, 10, 12 and G14 gave the highest results. The weekly measured growth performance parameters (body weights, body gain, and feed conversion ratios) were improved by the supplementation of probiotic and probiotic product either singly or being combined, also these compounds improved the performance parameters when being administered with vaccine. All these results confirmed that the addition of probiotic or probiotic product, either singly or in combination with vaccination regimen have immunomodulatory properties, improved the haematological parameters and lowered the mortalities at the beginning of rearing age and after challenge with a mixed culture of E.coli O78 and E.coli O26, Salmonella Typhimurium, Salmonella Enteritidis.