الفهرس 
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Abstract
A total of 450 milk samples were collected from apparently normal of udder Friesian lactating cows were investigated for subclinical mastitis. These animals were subjected to California Mastitis (CMT), Electric conductivity (ECT) and pH indicator paper (pHI) tests. Milk whey were prepared from the positive reactors as well as another 50 samples from negative subclinical cases used as control were subjected to Catalase, Nitric oxide, Lysozyme and Electrophoresis determinations. Bacterial examinations of 166 quarter milk samples that reacted
positively to different field screening tests used to evaluate the efficiency tests and detect its sensitivity. The results showed that 6.2%, of examined cows and 3.2 % of examined quarter were positive for CMT with different scores. While 8% of the examined cows and 3.8% of the quarters reacted positively to ECT with conductivity of 9 m/sc. or more. pH indicator paper test showed 3.8% cows and 2.1% of examined quarter were positively with variable degree of intensity of colour. Immunoanalysis for some components of the milk whey from the positive reactors were applied and compared with the normal milk whey values. Milk whey samples from the subclinical cases showed 15 folds, 2 folds and 3 folds significant increase in the main value of catalase, nitric oxide and lysozymes respectively as compared to control samples. Protein fractions & profile of milk whey detected by electrophoresis revealed a significant increase in alpha lactoglobulin level. Bacterial examinations revealed that 62.7%, 75.4% and 68.4% were positive to the above screening tests respectively. E. coli was the more common environmental strain isolated in 37.3% of the examined samples as a single isolate and in 15.7% in combined with other bacteria. This is followed by Streptococcus dysgalactiae in 12.2% of the samples as a single strain and in 6.1% in a combined form. Other environmental pathogens isolated were S. uberis (8.7%), Pseudomonas aeruginosa (7.8%), Klebsiella pneumoniae (6.1%) and Enterococcus faecalis (5.2%) isolate and in 13.0%, 4.3%, 5.2% and 0.9% in combined form respectively with other strains. Antibiotic sensitivity test was carried out and the results showed that tetra delta, norfloxacin and gentamycin were more efficient in their antibiotic activity on most of the isolated strains. A field trial was done to treat the subclinical case detected by screening tests using non therapeutic method. This was applied by increased frequency of milking of the affected animals up to 6 frequencies milking daily for three consecutive weeks. The results showed that the percentage of cured animals after one week was 54.2% as detected by CMT, 66.7% by ECT and 63.2% by pH indicator paper. After two weeks these percentages were 23.8%, 29.0% and 26.3% respectively. After three weeks these percentages were 18.6%, 4.3%, and 10.5 respectively. Percentage of non cared animals after three weeks of frequent milking were 3.4% as detected by CMT only.