الفهرس 
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Abstract
Subclinical mastitis is considered as one of the most costly diseases in dairy production throughout the world; therefore more attention has been focused for its diagnosis. This study was conducted to establish the prevalence of subclinical mastitis (SCM) in two dairy herds located in Ismailia and El-Sharakia Governorates with isolation of some causative microorganisms. About 230 quarter milk samples (QMS) were collected from apparently healthy hundred cows and subjected to California Mastitis Test (CMT), 130 (56.5%) of the examined samples reacted negatively to CMT, while 100 (43.5%) were CMT positive. The mean milk somatic cell count (MSCC) of the positive samples was (1.1 X 106 ± 61554.12 cells/ml.). The mean Koestler value and acidity % of the examined milk samples were 4.62 ± 0.08 and 0.199 ± 0.013 %, respectively. Lactate Dehydrogenase (LDH) enzyme level was determined in the examined quarter milk samples and in blood serum with mean values of 621.15 ± 55.45 and 633.17 ± 30.20 (U/L), respectively. Staphylococci, Coliforms and Streptococci were present in 100, 100 and 88% of the examined positive CMT quarter milk samples, respectively. The results of Polymerase Chain Reaction (PCR) test revealed the isolation of S.aureus, Sreptococcus agalactiae and E. coli strains with percentages of 4.35% , 21.74% and 1.36%, respectively.