Epidemiological Investigation Of Subclinical Mastitis In Nanjing, Study Of Pathogens And Detection Of Multiplex PCR

Bovine mastitis led large loss to the dairy industry. Generally, bovine mastitis was classified into clinical mastitis and subclinical mastitis. Subclinical mastitis showed little symptom and was diagnosticated by certain detection assay. The incidence of subclinical mastitis is 20% to 50% in developed countries, while 50% to 80% in our country. Subclinical mastitis resulted in marked reduction in milk production, and 70% of loss resulted from mastitis can be due to subclinical mastitis. So, study of preventive and diagnostic measures to control subclinical mastitis was of highly significance. This study was based on epidemiology of subclinical mastitis, pathogens and rapid detection. The main results were followed:1 With analysis of the data on DHI of a dairy farm in a year, the effect of age, seasons and lactation stage on SCC in raw milk and the incidence of subclinical mastitis was evaluated. The results showed that age might effect obviously on SCC and the incidence of subclinical mastitis. With age increasing, SCC and the incidence of subclinical mastitis rised. While lactation stage and seasons had little effect on SCC and the incidence of subclinical mastitis.2 SCC in raw milk was regarded as the diagnostic criteria to bovine subclinical mastitis. 88 dairy cows were detected intramammary infection (IMI) by SMT and SCC. The results of detecting by SMT were contrasted to the results of detecting by different threshold of SCC, and the concilient rate of SMT to SCC was calculated. When 300,000 cells/mL as diagnostic threshold of SCC, the concilient rate was the highest, to 46.88%.3 104 milk samples were collected from dairy cows suffering from subclinical mastitis on three dairy farms in Nanjing. 93 strains of bacteria were isolated and identificated. The pathogenic bacteria were mainly cassified to Staphylococcus, Streptococcus and coliform. 8 strains of coliform, 10 strains of Streptococcus and 16 strains of Staphylococcus were analyzed with the antimicrobial disk susceptibility test, hemolysis test and cytotoxicity test. The results indicated that the main pathogens wereresistant to several drug. Most Staphylococcus were shown to be strongly haemolylic activity, but the other bacteria were shown to be slightly or little haemolylic activity. One strain of coliform and two strains of Staphylococcus were shown to be cytotoxic to Vero cell, and 9 strains wee shown to be cytotoxic to Hep-2 cell.4 Multiplex polymerase chain reaction assay was developed for detection of Staphylococcus aureus and Streptococcus agalactiae causes of bovine mastitis. The PCR was optimized and the specificities and sensitivities of the PCR were analyzed. DNA extracted by boiling, 12 strains of Sta. aureus and 10 strains of Str. agalactiae were detected by the PCR. Expecting fragments were amplified from all strains. 54 milk samples from cows suffering subclinical mastitis were detected by the PCR and conventional bacterial identification. Staphylococcus aureus and Str. agalactiae were detected by the PCR from 12 milk samples and 14milk samples, respectively. While Sta. aureus was isolated from 13 milk samples and Streptococcus agalactiae from 17.