85
Prevalence of Bovine Mastitis Pathogens in Bulk Tank Milk
Bovine mastitis is the most significant disease of dairy herds that can cause huge economic losses in the world. The objective of this study was to assess the bacteriological quality of bulk tank milk at herd level. Bulk tank milk samples collected from 894 dairy herds in Inner Mongolia (375), Heilongjiang (242) and Hebei Province (277) of China were examined for the presence of mastitis pathogens from March 2012 to May 2013. Each sample was tested using a previously validated Multiplex PCR assay for the detection of 12 pathogens at a time. In addition, a maximum of 21 samples were examined simultaneously using the Multiplex PCR assay. Contagious pathogens including Streptococcus agalactiae (90.16%), Coagulase negative staphylococci (89.17%), Streptococcus dysgalactiae (71.14%), Arcanobacterium pyogenes (60.51%), Staphylococcus aureus (44.85%) and enviromental pathogens consisting of Coliforms (63.26%) and Escherichia coli (31.66%) were detected in the milk samples. Of the 894 bulk tank milk samples, 743 (83.11%) contained four or more species of bacterial pathogens. It was also observed that an increase in the frequency of isolation of bacterial pathogens was significantly associated with an increased bulk tank bacterial and somatic cell counts. Bulk tank milk with lower bulk tank bacterial and somatic cell counts had fewer species of bacteria. Herd size and farm management practices had considerable influence on the species of bacteria, bacterial and somatic cell counts in bulk tank milk. The percentage of small herd (size＜50 cows) with four or more types of bacterial pathogens detected in milk samples was higher than that of big herd (size＞500 cows), which was 86.45% and 71.79%, respectively. 85.20% (501/588) of bulk tank milk samples had four or more types of bacterial pathogens in winter, while the percentage was 88.89% (272/306) in winter. There were no differences in the species of bacteria in bulk tank milk between summer and winter. In conclusion, species of bacteria, bacterial and somatic cell counts could serve as indicators of the quality of bulk tank milk and we should formulate strategies to improve milk quality and reduce the incidence of mastitis on dairy herds.
Keywords: bulk tank milk, bovine, mastitis pathogens