الفهرس 
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Abstract
This study was carried out to determine the prevalence and the potential risk factors associated with the occurrence of mastitis in dairy herds, identifying the bacterial causes of mastitis, conducting antimicrobial susceptibility test on bacterial isolates and finally to establish a new approach for prevention and control of disease in dairy herds to submit this program as a pilot model for milk producers and veterinarians in study area.
Part (I): Occurrence and risk indicators of mastitis in dairy farms
This part was conducted in two private dairy farms in Beni-Suef district during the period from April ,2009 till the end of November ,2011. A total of 350 apparently healthy and clinically mastitis cows of different breeds (117 Friesian and 233 Holstein cows) were included in this study. The udders of all milking cows in both surveyed farms were examined clinically and by CMT for detection of subclinical mastitis at cow’s and quarter levels. Samples were collected from both milking cows and their surrounding environment in examined farms whereas individual quarter milk samples were analyzed for somatic cell counting and bacteriological examination. Environmental samples includes swabs from interior of teat cups, milker’s hands, water used for washing milk utensils & for drinking besides soil from yards that in contact with dairy cows.
A structured questionnaire was prepared and information regarding the prevalence and risk indicators of mastitis in both dairy herds including those attributed to cows such as previous history of mastitis& tick infestation and farms such as farm hygiene & milking practices. The questionnaire revealed several positive aspects in farm (II) includes farm hygiene, application of California mastitis test (once/ month), washing of udders of all cows before milking, besides veterinary supervision coverage.
The obtained results showed that:
1. Prevalence of mastitis were higher in farm (I) at both cows and quarters levels (55.61 % 34.72 & resp.,) compared to that (29.28 & 42.92 resp.,) in farm (II). Moreover, the percentage of clinical mastitis were also higher in farm I (13.7 % & 9.8 % resp.,) compared to farm II (8.19 % & 5.8 % resp.,).
2. The highest percentage of cows quarters undergoes subclinical intramammary infection showed weak positive (1+) in both farms (97.46 & 98.6 % resp., while the least quarters had negative reaction (0. 8 & 0.52 resp.,) evenly, the CMT reacted distinctly and strong positively (2+ & 3+) with clinically mastitic quarters in both farms (100.0 % of each)
3. The validity of CMT in detection of bacteriological positive quarters in farms (I&II); it revealed that test sensitivity were (98.0% &98.87% resp.,) while specificity were (98.05% &98.5% resp.,) in examined farms
4. Moreover, Coagulase negative staphylococci (CNS) was the primary causative agent for subclinical mastitis in dairy cows of farms I&II (42.86 & 45.99% resp.,) followed by Staph.aureus (25.89 & 23.53 % resp.,), Strept.agalactiae (16.96 & 13.9 % resp.,), E.coli (11.6 & 11.76 % resp.,) .On the other hand, E.coli was isolated in highest rate from clinical mastitis quarters in both farms ( 51.4 & 44.4 % resp.,) followed by Staph.aureus (29.73 & 33.3 % resp.,),Strept.uberis (13.5 & 7.4 % resp,).
5. The average somatic cell count (±SE) was higher in Holstein breeds compared to Friesian. Moreover an average count (216.422± 9.42 & 325.937±12.38 x 103cells /ml resp.) can be used as index for prediction of occurrence and severity of mastitis in both breeds.
6. Cow’s environment represents a potential source for mastitis causing agents which survive in higher percentage in farm I (42.0 %) compared to (36.3 %) in farm II. Moreover, soil appeared that the primary source of bacteria causing mastitis mostly E.coli & Klebsiella.spp resp., while teat cups & milkers hands posed a potential source for contagious pathogens; CNS ,Staph.aureus & Strept.agalactiae resp., Meanwhile water in dairies had potential role in spreading of E.coli ,Staph.aureus & CNS resp.,
7. Results indicated that cow’s breed and age were significantly affects on prevalence and severity of mastitis in milking cows of examined farms. Moreover, Friesian breed had a higher risk of developing mastitis (SCM & CM) compared to Holstein breed at (p<0.01, 0.001).
8. Moreover, results referred to lactation stage & parities as potential risk factors predispose to disease occurrence as at early lactation stage and at the period of involution of the mammary glands were the most susceptible stages with prevalence of (60.68 & 45.5 % resp.,) and (56.63 & 43.04 % resp.,) and lower in mid lactation (49.12 & 36.1% resp., ) at p<0.05 and p<0.001 indicating the possibility of encountering mastitis in early stage of lactation.
9. Season of year was found to exert a significant effect on prevalence of mastitis; higher positive findings mostly contagious pathogens were obtained in summer and spring (50.82 %, 35.09% respectively), that was significantly (p< 0.001) different than those encountered in autumn and spring (18.52 & 30.83% resp.,) meanwhile in farm (II) higher positive findings mostly contagious pathogens were recorded during summer and spring also (36.25 % & 31.6%resp.,) that was significantly (p< 0.001) different than those encountered in autumn and winter (17.65 %& 31.82 % resp., ) .
Results in part (I) revealed the extreme importance of determining the potential risk factors predisposing mastitis occurrence, early detection of subclinically mastitic cases besides routine culturing of milk samples from apparently healthy and mastitic quarters for isolation and identification of mastitis producing agents.