الفهرس 
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Abstract
Subclinical mastitis has been considered the most important problem in dairy farms all over the world. Decrease of milk yield is the major fraction of financial losses in addition to other causes. Adoption of subclinical mastitis (SCM) control programs are seen in many countries. The current diagnosis of SCM depends on the detection of inflammatory reaction and microbial culturing. Somatic cell count (SCC) is now the screening tool for the inflammatory reaction and as there are many other effectors that may alter SCC, another screening tool is required to be used instead of SCC or together with it.
The study was applied on 528 bovine quarters’ milk samples of 137 Holstein Friesian cows belonged to two groups of herds. 338 quarter milk samples of 85 cows from large, organized and intensive farm herds (group A) and 190 samples of 52 cows from small, medium non-organized farms and small holders’ herds (group B).
On relative to total examined quarters, SCM quarters and recovered isolates, S. dysgalactiae was the most isolated pathogen and constituted 13.66 %, 32 % and 26.85 % followed by S. epidermidis (7.77%, 18.2% and 5.29%) then S. saprophyticus (7.56%, 17.7% and14.87%), E. coli (7.35%, 17.2% and 14.46%), S. uberis (5.25%, 12.3% and 10.33%), S. aureus (3.6%, 8.37% and 7.02%), S. agalactiae (2.31%, 4.41% and 4.56%) and Proteus vulgaris (2.1%, 2.9% and 4.13%) respectively. At last, each of B. cereus, M. luteus and P. aeruginosa constituted 0.42%, 0.98% and 0.83% respectively.
In group A, the most isolated was S. dysgalactiae (25.8%) followed by S. epidermidis (16.1%), S. saprophyticus (14.8%), E. coli (12.9%), S. uberis (1.96%), S. aureus (10.3%), and S. agalactiae (3.2%).
In group B, the most obtained isolates were S. dysgalactiae (28.7%) followed by E. coli (17.2%) then S. saprophyticus (14.9%), S. epidermidis (13.8%), S. uberis (9.2%), Proteus vulgaris (6.9%) and S. agalactiae (6.9%).
Geometric mean of the SCC in group (A) was higher than that of the group (B) which were 548000 and 455000 cell/mL respectively.
Geometric mean of lactate dehydrogenase (LDH), Glutamic oxaloacetic transaminase (GOT) and alkaline phosphatase (ALP) were 378, 147 and 469 IU/L respectively. Higher LDH, GOT and ALP mean in case of SCM in the organized farm group (419, 158 and 488 IU/L respectively) in relative to non-organized farms group (359, 150 and 446 IU/L respectively).
PCR amplification and gene detection were conducted on the extracted DNA of the isolated pathogens. Detection of the amplified products of E. coli (231bp), S. agalactiae (280 bp), S. aureus (108 bp), S. epidermidis (124 bp), S. dysgalactiae (270 bp) and S. uberis (330 bp) revealed a confirmation of 100%, 72%, 40%,73%, 75% and 100% of isolates respectively.
More strong significant positive correlation of ALP (r (203) = 0.50, P = 0.001) with SCC in screening samples in comparison with LDH (r (203) = 0.174, P = 0.01.) and GOT (r (203) = 0.317, P = 0.001).