الفهرس 
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Abstract
The aim of this study is to measure the frequency of occurence of salmonellosis in some feedlot calves farms in Egypt, and identifying the different risk factors play a role in the likelihood of perpetuation of this organism among calves on these farms provide a scientific basis for the development of practical preventive measures. The point prevalence in different farms and different localities revealed that the prevalence were 0%, 3%, 1.8%, 0%, 0%, 2.5% and 1.8% in farms A, B, C, D, E, F and G respectively, and 1.36% from Qalioubia governorate, 0.87% from Monofia governorate and 2% from Sharkia governorate. The overall individual level prevalence of bovine salmonellosis in feedlot calves farms were 1.28%. Among 7 enrolled herds, 4 (57.14%) yielded Salmonella-positive samples during the study period. Risk factors identification of bovine salmonellosis using statistical software programe one way ANOVA test revealed that the risk factors that were found to be associated with the presence of this pathogen included purchasing calves from dealers (OR. 6, 95% CI. 1.00 to 46.00 and P< 0.001), herd size 100 and more (OR. 1.5, 95% CI. 0.7-7.38 and P< 0.025). group housing (OR. 3.5, 95% CI. 1.00-16, P< 0.02 ), dirty muddy calf floor area (OR. 2.6, 95% CI. 0.5-12.8, P< 0.012), inadequate cleaning of feeding and watering utensils (OR. 3.5, 95% CI. 0.7-9.77, P< 0.005), rodents in feed storage area (OR. 3.6, 95% CI. 0.7-9.52, P< 0.001), presence of dogs and cats (OR. 1.5, 95% CI. 0.8-7.38, P< 0.034), lack of barn disinfection (OR. 3.38, 95% CI. 0.65-17.2, P< 0.003), age of calves (OR. 7, 95% CI. 1.00-13.9, P< 0.012), breeds (OR. 1.5, 95% CI. 0.7-7.18, P< 0.023), gender (OR. 1.5, 95% CI. 0.7-7.33, P< 0.034), season (OR. 1.3, 95% CI. 0.65- 8.00, P< 0.015). Bacteriological isolation of Salmonellae from diseased and apparently healthy calves revealed that all the seven identified cases are isolated from diseased diarrheic calves in percentage of 7%. On contrary no Salmonella could be isolated from apparently healthy calves. The presence of diaherria increased the risk of Salmonella fecal shedding, (OR. 7.5, 95% CI. 1.00-22, P< 0.001). The biochemical identification of the isolated strains using Viteck II system revealed that all were identified as Salmonella spp, with accuracy up to 99%. Serotyping of the seven isolated strains revealed that they were identified as S.enteritidis. All Salmonella strains were examined using real- time QPCR. Two oligonucleotide primers were used for amplification of a 150 bp streatch of invA gene of Salmonella spp. 40 PCR cycles were performed with denaturation at 95°C/20 sec., annealing at 58°C/30 sec and extension at 72°C/30 sec. InvA gene was present in all detected bovine Salmonellae. and can be used as a valuable, diagnostic tool for detection of bovine Salmonellosis. RAPD PCR was applied for identification of Salmonella. The amplification plot of the seven isolated strains revealed that RAPD PCR is accurate and rapid method, it utilize a premade primers and probe for identification of Salmonellae from purified colonies just in 30 min..