الفهرس 
Introduction
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Abstract
The current study was aimed to detect the prevalence of bovine mastitis in Dakahlia and Damietta Governorates, Egypt and risk factors for its high prevalence. Besides, evaluate the role of oxidative stress biomarkers, antioxidant enzymes and metabolites as possible bio-markers for acute clinical mastitis in dairy cows. A total number of 116 dairy cows aged between three to ten years old were included in this study. from which, 100 cows exhibited the clinical signs of mastitis. In addition, 16 apparently clinically healthy cows were randomly selected and served as a control group for this study. The samples were collected in the period between May, 2014 and January, 2015 where 96 samples were collected from Dakahlia as well as 20 samples from Damietta Governorates, Egypt. The obtained results, in this study revealed that, all clinically examined dairy cows showed a significant increase in the clinical index score. In addition, the current study gave an isolation profile for the most prevalent pathogens. In general, the large percentage of isolation was for the mixed infection 118/159 (74.21%) between Staphylococcus spp., Streptococcus spp., and E.coli. then isolation percentage, came to be forE. coli 15/159 (9.43%) then for Staphylococcus aureus13/159(8.18%),coagulasenegative staphylococcus 8/159 (5.03%), Streptococcusagalactiea3/159(1.89%) and Streptococcus dysgalactiea2/159 (1.26%). Regarding the level of different oxidative stress markers and enzymatic antioxidants activity in clinical mastitis, there was a significant decrease in SOD, Catalase activity and TAC compared to control group. Whereas there was a significant increase in MDA and GR compared to control ones. Regarding different antioxidant trace elements levels in clinical mastitis, there was a significant decrease in Zn level compared to control group. Whereas there was a significant increase in Cu level comparatively to those of the control ones.With regard to the correlation between different biochemical parameters in clinical mastitis. The obtained results pointed out that there was significant correlation between SOD and CAT, MDA, TAC; CAT and SOD and TAC; MDA and SOD; TAC and SOD, CAT and Zn; Zn and TAC.