الفهرس 
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Abstract
The present trial conducted to evaluate the efficacy of usage of silver nanoparticles (Ag-NPs) and sodium butyrate (Na-B) encapsulated in palm fat as antimicrobial alternatives. Therefore, the inhibitory effect of Ag-NPs against E.coli was determined in vitro. Then, the effects of its use (in different doses) and sodium butyrate on experimentally induced colisepticaemic broiler chickens for a period of 35 days were studied in vivo through measuring the clinicopathological assay (daily) and performance variables (weekly) in addition to some measurements at the end of experiment like gross lesions scoring; related organ weight; E. coli re-isolation; E. coli virulence gene expression by rt-qPCR; morphological characterization of E.coli using (TEM) and histopathological examination. In vitro study was carried out by Disk diffusion method by using pure form of Ag-NPs (2000 ppm) and other concentrations (200, 20, 2, 10, 5, 2.5 and 0 ppm). then, in vivo study was done using one day-old Cobb chickens (n = 180) allotted randomly into 6 equal groups (1-6). Each group consisted of 30 birds with 3 replicates of 10 each. The chickens fed mash diet for 3 phases: starter (day 0:17), grower (day 18:28) and finisher (day 29:35). Chickens of group1, 2 and 3 were supplemented with Ag-NPs 4ppm, 6 ppm and 8 ppm, respectively. Chickens of group 4 were supplemented with Na-B from day old till end of study in doses of 1, 0.5 and 0.25 Kg/MT of feed in the starter, grower and finisher ration, respectively. Chickens of group 5 were kept as positive control group (infected and non supplemented) while those of group 6 served as blank control. For experimental induction of colisepticemia; experimented chickens of groups 1-5 were individually infected by crop gavages with 6×108 CFU/ml of E. coli serogroup O78 for 2 successive days (14th and 15th of experiment) with 0.5 ml/bird/day.
Regarding to the results, Ag-NPs had a potent inhibitory effect (in vitro) against E.coli growth in pure form only (2000 ppm), while in vivo study we noted that supplementation of the lower dose (4ppm) led to improvement in the colisepticaemic chickens performance, downregulation in virulence genes expression, reduction of both gross and histopathological lesion scores and alteration of electromicroscopic profile of the inoculated E.coli. Severe toxicity recorded by supplementing the highest dose of Ag-NPs (8ppm) that resulted in bad effects on all measured parameters except the gene expression. Similarly, Na-B had the same beneficial effects of Ag-NPs (4ppm) on all aforementioned measured parameters except in case of gene expression where Na-B had showed a better effect.
Conclusively, Ag-NPs and Na-B have potent antimicrobial effect but Ag-NPs may be toxic to the birds in high doses (dose dependent). However, as public health is on the top of priority, we recommended usage of Na-B. Regarding some references, we are cautioning against the use of Ag-NPs until be sure on absence of residues in chicken’s tissues. For confirmation of safety of Ag-NPs further studies should be conducted with cautions during its handling. We also recommend using one source (producer) for these nanoparticles studies in EGYPT to take a decision for its usage as feed additives or disinfectant only or even banning its use.