Comparison of incidence of three major pathogens causing bovine subclinical mastitis in relation to SCC and enzymatic activities in large and small dairy herds in Egypt.

The study was designed to investigate the current incidence of Staphylococcus aureus, Streptococcus agalactiae and Escherichia coli in bovine subclinical mastitis (SCM) in two groups of herds, large dairy herd: group 1 (≥100 head/farm) and small and medium dairy herds: group 2 (≤50 head / farm + small owner's herds) in Egypt. S. aureus and S. agalactiae are contagious major pathogens of mastitis, while E. coli is an environmental major pathogen. PCR amplification and gene detection were carried out on the extracted DNA of the pathogens' isolates which were identified by conventional methods. Three pairs of specific primers, one for each of the pathogens were used in PCR amplification. Detection of the amplified three products of sizes 231 bp, 280 bp and 108 bp resulted in confirmation of 100%, 72% and 40% of isolates of the E. coli, S. agalactiae and S. aureus respectively. Additionally, the study referred to the associated variable values of somatic cell count, enzymatic activities of lactate hydrogenase (LDH), glutamic oxaloacetic transaminase (GOT) and alkaline phosphatase (ALP). The study included examination of randomly selected 476 of apparently normal milk samples belonged to 137 apparently healthy Holstein Friesian cows. Incidence of SCM was 42.6% of the examined quarters and 62% of cows represented by 203 samples and 85 cows with the result of recovered 242 isolates. In relative to total number of examined quarters, SCM quarters and total number of isolates, S. agalactiae constituted 2.31 %, 5.41% and 4.54 % while S. aureus was 3.6%, 8.37% and 7.2% whereas E. coli represented 7.4%, 17.2% and 14.5% respectively. SCC Geometric mean of SCM samples in the overall study was 483000 cell/mL. In the present study, the higher SCC mean was in SCM samples with S. aureus (611000) followed by E. coli (545000) then S. agalactiae (394000). Geometric mean of LDH, GOT and ALP were 378, 147 and 469 IU/L in the overall study SCM samples. The higher mean of LDH was recorded in case of S. aureus (402) followed by S. agalactiae (398) then E. coli (369). The higher GOT value was in case of S. agalactiae (150) followed by E. coli (149) then S. aureus (147). The higher ALP value was in E. coli (614) followed by S. aureus (560) then S. agalactiae (553). [ABSTRACT FROM AUTHOR]