الفهرس 
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Abstract
In this study, Six hundred embryonated egg samples of early embryonic death (300 egg samples) and dead-in-shell embryos (300 egg samples) were collected from 3 balady breeds (Dahabi, Matrouh and Fayoumi). In early embryonic deaths samples, bacterial isolation rates were 30%, 100% and 60% from Fayoumi, Matrouh and Dahabi breeds, respectively. Meanwhile, dead-in-shell embryo samples revealed a 100% isolation rates from all breeds. The total number of bacterial isolates obtained from isolation was 190 isolates from egg samples containing embryo dead in early stage of incubation. Isolated bacteria were Proteus spp. (90 isolates), E. coli (40isolates),Klebsiella spp. (18 isolates), Pseudomonas spp. (22 isolates), Citrobacter diversus (10 isolates) and Enterobactercloacae(10 isolates). Another 300 bacterial isolates were obtained from dead-in-shell embryos samples. Isolates were Proteus spp. (100 isolates), E. coli (40isolates),Klebsiella spp. (30 isolates), Pseudomonas spp. (37 isolates), shigella spp. (30 isolates), Edwardsiella spp. (20 isolates), Citrobacter diversus (12 isolates),Enterobactercloacae (15 isolates), Citrobacter freundii(11 isolates) and Serratia spp. (5 isolates). Sero-grouping of the isolated E. coli strains 80 isolates from(early embryonic death samples and dead-in-shell eggsamples), revealed O146, O78, O125, O26, O81 and un-typed strains from dead-in-shell embryo samples with prevalence of 33.7%, 26.2%, 18.7%, 8.8%, 3.8% and 8.8%, respectively.
In this study, the antibiogram test was carried out against tested microorganisms that used in experimental infection test (P. mirabilis, E.coli O146). P.mirabilis showed resistance to ampicillin and sulbactam, colistin sulphate and streptomycin. However tested E. coli O146 was resistant to colistin sulphate, nitrofurantoin, gentamycin and streptomycin.
Experimental dipping of embryonated eggs at two different stages of egg incubation (at 3rd day of egg incubation and 18thday of egg incubation) was conducted to study effect (pathogenicity) of selected pathogens as single or mixed infection on hatchability and hatched chick’s clinical signs, post-mortem signs, performance and histopathology of internal organs. Hatchability was calculated after 21 days of incubation. The hatchability rate was lower in incubated eggs infected at the 3rd day of egg incubation with E. coli O146, P. mirabilis and mixed infection (56.7%, 46.7%, and 40%, respectively). Relatively better hatchability rates of (76.7%, 70%, and 63.4%) for eggs infected at 18th day of incubation. Dead-in-shell eggs after infection had offensive odor. Embryos showed septicemic picture, congested visceral organs.
Hatched chicks showed dullness, depression, ruffled feather (mushy chick) and white diarrhea. Mortality observed at first week post-hatch was 17.6%, 28.5% and 33.3% in eggs dipped at 3rd day of incubation in E. coli O146, P. mirabilis and mixed infection groups, respectively. Mortality rates were 13%, 14% and 21% in groups infected at 18th day of incubation, respectively. Apparently healthy chicks showed lower performance than un-infected controls chicks. Clinical signs varied in severity from group to another with high severity in group with mixed infection. Significant low body weights were reported at all-time points.Histopathologically, the main lesions reported in dead in shell embryos (both field samples and experimental dipping with E. coli and P. mirabilis) were necrosis of hepatocytes, portal and sinusoidal thrombosis with bacterial invasion and sever inflammatory cell infiltration with sever vasculitis, pericarditis and myocarditis, yolk sac congestion, and thickening of yolk sac wall. Intestine showed necrosis of mucosa that may extend to musculosa, inflammatory cell infiltration and congestion of intestinal blood vessels. In hatched chicks at either 14 or 28-day old, there was liver congestion with mild perivascular edema and thrombus formation which consisted of fibrin threads and bacteria. Degeneration of hepatocyte, myocardial degeneration, yolk sac wall thickening wall and filling with caseated material, granuloma formation, and intestinal necrosis of mucosa, congestion of intestinal blood vessels with inflammatory cells infiltration and thickening of serosa.These lesions varied in degree and as expected was more sever in mixed infection groups.
To conclude:
- E. coli and P. mirabilisare the most prevalent bacterial species isolated from dead-in-shell embryos indicating their importance as a major cause of egg hatchability problems in poultry farms.
- Expermintal dipping of embryonated eggs at different stages of incubation indicated that both pathogens have a direct effect on hatchability.
- Mixed infection of E. coli O146 and P. mirabilis has more prominent impact on both embryo mortality and hatched chick.
- Infection withE. coli O146 and P. mirabilis causedearly chick’s mortailities and reduced performance of hatched chicks.
- The hatchery sanitation is a critical step to reduce losses associated with infectious bacteria causing low hatchability.