الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In dairy herds, the percentage of SCM may reach up to 75% and the economic losses are largely attributed to loss of milk production, costs of treatment and early culling. Affected animals with SCM showed decreased milk production and altered composition of the secretion with presence of an increased number of bacteria and somatic cells, but in contrast to clinical mastitis without any visible changes in milk and udder.
The diagnosis of mastitis is based on the SCC and microbiological status of the quarter. Bacteriological culture of milk samples is the standard method for identifying mastitis. Direct cell count and sorting cell count may avoid difficulties associated with bacteriological examination of the milk. Leukocytes from foremilk samples could be counted and differentiated simultaneously using flow cytometry and due to the rapid characterization of a large number of cells as well as the definite identification of individual cell populations using specific antibody, flow cytometric analysis gives more accurate results compared with other tests of SCC and helps for planning of appropriate therapeutic interventions.
Objectives of the present study were;toapply a recent trend for diagnosis of SCM using flow cytometry for direct counting and sorting somatic cells, to screen for the most incriminated pathogens of bovine subclinical mastitis, and to determine the changes in levels of oxidative stress and antioxidant system through determination of concentration of malondialdehyde and total antioxidant capacity, respectively in blood and milk of cows with subclinical mastitis.
The present study was carried out on 75 lactating dairy cows (Holstein/Frisian). These cows were housed in different governmental and private farms within the territory of Assiut Governorate.Milk samples (30 ml each) from each quarter (n=280) were collected aseptically in sterile containersto find the percentage of SCM on the basis of quarter.At the laboratory, the sample was tested for subclinical mastitis using California Mastitis Test (CMT) and divided into 3 parts for microbiologic examinations, flow cytometric analysis and tested for oxidative stress biomarkers.Two blood samples (5- ml for each) were collected by jugular vein puncture using sterile disposable syringes. One for estimation of plasma levels of Total Antioxidant Capacity (TAC) and the other for estimation of serum levels of Lipid Peroxide (MalondialdehydeMDA). The data were statistically analyzed using computer software.
Results showed that the average age of cowsunder investigation was 3.9 years. The average number of parturitions (parity) in cows was 2.25. The average number of milking seasons was 3.7. Cows were classified into control group (n=20) and cows with subclinical mastitis (n=55) according to the results of California Mastitis Test.A total number of 280 milk samples were classified according to results of California Mastitis Test into negative (n=80) from 20 healthy cows, one positive (n=85), two positives (n=50), and three positives (n=65). Results of microbiological examination revealed isolation of 3 microorganisms; Streptococcus species (n=25, 19.23%), Staphylococcus species (n=70, 54%) and E. coli (n=65, 50%). Results of flow cytometric analysis revealed significant increase in inflammatory cells in milk of cows with subclinical mastitis if compared to normal control cows. Flow cytometric sorting of inflammatory cells in milk of cows with subclinical mastitis revealed a significant increase in neutrophils count and percentage in comparison to normal milk.There was significant decrease in plasma and milk level of TAC and significant increase in concentrations of serumand milk MDA of cows with subclinical mastitis.