الفهرس 
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Abstract
In the present work a total of 420 lactating Holstein cows in three dairy farms at Damietta (farm A, 120 lactating cow and farm C, 160 lactating cow) and El-Sharkia (farm B, 140 lactating cow) governorates in Egypt; were examined for clinical and subclinical Staphylococcal mastitis and also vaccinated by Staph. aureus bacterin and were observed during the period from May 2013 to December 2016. from etiological point of view, the current bacteriological examinations revealed that the total number of Staph. aureus isolated from milk samples of clinical quarters were 56 isolates, while the total number of coagulase negative staphylococci were 133 isolates with total prevalence rate of 19.5% and 46.5%, respectively. Also the results for subclinical mastitis revealed that the total number of Staph. aureus isolated from milk samples of sub clinical quarters were 233 isolates, while the total number of coagulase negative staphylococci were 324 isolates with total prevalence rate of 32.1% and 44.6%, respectively. In the present work, between 1012 clinical and sub clinical mastitic quarters total prevalence rate of Staph. aureuswas 28.6%. While the total prevalence rate of coagulase negative staphylococci was 45.2%. Concerning to vaccination with Staph. aureus bacterin, after vaccination (after the 120 day from vaccination and at the end of the trial) the overall prevalence rate of clinical mastitic quarters among vaccinated cows at the level of quarter was reduced to 11.8% (192/1630), while the overall prevalence rate of subclinical mastitic quarters among vaccinated cows at the level of quarter was reduced to 30.06% (490/1630).
In respect to the effect of Staph. aureus bacterin on total prevalence rate of Staph. aureus and coagulase negative staphylococci isolated from clinical and sub clinical mastitic quarters, the total prevalence rate of Staph. aureus was reduced by 40.1% , and the total prevalence rate of coagulase negative staphylococci was reduced by 36.9%. Also average of milk yield per cow was increased by 15.8%. Regarding to the effect of vaccination on bulk tank analysis, total bacterial count was reduced by 53.6%, SCC was reduced by 47.8%, total Staphylococcal count was reduced by 69.2%, Staph. aureus count was reduced by 95.1% and the percent of fat and protein was increased by 9.5% and 10.8%, respectively. Concerning to the effect of vaccination on culling rate per farm, the overall culling rate was reduced by 30.8%. Also effect of vaccination on frequency of new Staph. aureus IMI was observed and found that the total prevalence rate of new Staph. aureus mastitis was 10.3% at the level of quarter, while the total prevalence rate of coagulase negative staphylococci was 38.3% with total protection rate of 63.9% and 15.3% for Staph. aureus and CNS, respectively. Regarding to the effect of vaccination on immunoglobulin sera titers against Staph. aureus, vaccinated cows showed elevated immunoglobulin sera titers to Staph. aureus bacterin.