Investigation Of The Incidence Pattern Of Subclinical Mastitis In Dairy Cows And Detection Of Pathogenic Bacteria In A Large-scale Cattle Farm In Heilongjiang

Mastitis is the most important disease that endangers the development of the dairy industry,causing a decrease in milk production and lower milk quality.In recent years,the incidence of subclinical mastitis in dairy cows has gradually increased,bringing huge economic losses to the dairy farming industry and jeopardizing the development of the cattle industry.In a large-scale dairy farm in Heilongjiang Province,cows with healthy appearance in lactation were selected for the trial.From April 2021 to October 2021,the collected DHI data were used to investigate the relationship between different months and the incidence of subclinical mastitis on this dairy farm,and 659 lactating cows in the farm inventory were monitored to investigate the relationship between litter size,daily milk yield and days in lactation and the incidence of subclinical mastitis in cows.Because the DHI test is the incidence rate of cattle,the CMT method was used so as to compare different dairy areas with the incidence of cryptomastitis in cows 88 milk samples from the dairy areas with positive CMT test were tested for pathogenic bacteria by 16-plex Q-PCR to detect the main pathogenic bacteria infecting cows with cryptomastitis.The results showed that the incidence of cryptomastitis was highest in August and lowest in May,with highly significant differences(P<0.01).there was a positive correlation between the number of litters and the incidence of cryptomastitis in cows,with the incidence of cryptomastitis increasing with the number of litters,with the lowest incidence in 1 litter(4.20%)and the highest incidence in 5 litters and above(21.43%),with highly significant differences between the litters(P<0.01).The highest incidence of subclinical mastitis(25.93%)was observed when the daily milk yield was less than 15 kg,and the lowest incidence(6.03%)was observed when the daily milk yield was 30-45 kg,with a highly significant difference(P<0.01).The lowest incidence(6.21%)was observed when the lactation days were 101-200 days,and the highest incidence(12.30%)was observed when the lactation days were less than 100 days,with a non-significant difference,the difference was not significant(P>0.05).The incidence of subclinical mastitis in the posterior breast area was significantly higher than that in the anterior breast area by the CMT method,and the difference was highly significant(P<0.01),while the difference between the incidence in the left and right breast areas was not significant(P>0.05).The detection rate of pathogenic bacteria in the 88 milk samples that were positive in the milk region of the cows tested by CMT was 78.41%,with slightly more infections with mixed pathogens(39.77%)versus single pathogens(38.64%),while pathogens causing elevated somatic cell counts were detected as coagulase-negative Staphylococcus(50%),yeast(50%),Escherichia coli(21.59%),udder Streptococcus(10.23%),Klebsiella(2.35%)and Cryptobacterium septicum(2.35%),all environmental pathogens.β-lactamase resistance genes were present at 60.23%.The incidence of cryptogenic mastitis on this farm was closely associated with month,litter size,daily milk yield,days of lactation,and milk area.The pathogenic species infected in this farm were mainly environmental pathogens.The milking operation process in this farm is relatively standardized,but the feeding management level still needs to be improved.