Study On The Application Of Lactobacilli-Based Teat Disinfectant For Preventing Subclinical Mastitis Of Dairy Cows

Subclinical Mastitis（SCM）is one of the most prevalent diseases of dairy cows in herds.This disease is usually caused by pathogenic bacteria invading the mammary gland through the cow’s teat.At present,pre-milking and post-milking teat disinfectants are applied to prevent SCM in the pasture.However,the traditional chemical teat disinfectants are unsuitable for long-term treatment of mastitis because of their side effects on drug residues.Therefore,it is necessary to develop a safe and effective chemical teat disinfectant alternative.At present,lactic acid bacteria have successful applications in the prevention of various diseases.So,the effectiveness of lactic acid bacteria in the treatment and prevention of SCM is an interesting research topic.In this work,11 cows with SCM were used as the research objects,lactic acid bacteria teat disinfectant（LAB）and chemical teat disinfectant（CD）were applied for cleaning cow teats before and after milking.In total,69 milk samples from cow teats were collected from the LAB and CD group,which were analyzed by Somatic Cell Count（SCC）,total bacterial counts,qPCR,third-generation sequencing,and untargeted metabolomics techniques,respectively.The changes were compared.The objective of this research was to comprehensively evaluate the effects of LAB disinfectant on the microhabitat of cow teats and the efficacies of the prevention of SCM.The results showed that both LAB and CD could reduce SCC in milk samples from cow teats,and the SCC of the LAB group was slightly lower than that of the CD group.Meanwhile,the bacterial and Staphylococcus counts in both groups reduced significantly,while the LAB counts increased.Furthermore,the increasement of lactic acid bacteria in the LAB group was greater than in the CD group.Moreover,q PCR results showed that the average content of three pathogens Escherichia coli,Staphylococcus aureus and Streptococcus agalactiae in the samples were significantly reduced after 10 days of cleaning with LAB,but the content of Lactobacillus increased.This illustrated that LAB can not only form a protective barrier outside the cow teat for preventing the invasion of external microorganisms.Meanwhile,LAB could also inhibit the growth of mastitic pathogens and improve the microhabitat of cow teat,and then it had a preventive effect on the occurrence of SCM in dairy cows.Based on the PacBio SMRT sequencing results,both LAB and CD milk samples from cow teat contained high microbial diversity,and the structure of bacterial community changed following the cleaning protocol.The relative abundance of some strains（Lactobacillus plantarum,Oceanobacillus profundus,Acinetobacter schindleri,Psychrobacter faecalis and Acidovorax radicis）had changed significantly.This suggested that these species could be used as markers of udder health.UPLC-Q TOF-MS-based untargeted metabolomics demonstrate that there were significant differences in the metabolites between LAB and CD groups.Compared with CD group,the average content of Vitamin B₂,malic acid and indole acrylic acid in the LAB group increased greatly,while Tyr-cys,L-palmitoylcarnitine and L-stearoylglycine declined.However,as the cleaning time increased,the metabolites profile of milk samples changed.Ten days after cleaning with LAB,the content of glucose,lactose and arachidonic acid increased greatly,but stearic acid,bile acids and most of the short peptides decreased significantly.The results showed that LAB could improve the microhabitat of cow teat by adjusting the composition of metabolites,which helped to enhance the defense function of the breast.