Etiological analysis of sow endometritis and screening of probiotic <italic>Lactobacillus</italic>

<bold>Objective</bold> The aim of this study was to explore the main pathogenic bacteria groups of sow endometritis and screen the probiotic strains which can be used for antibiotic replacement，thus providing reference for the prevention and treatment of sow endometritis. <bold>Method</bold> Bacterial 16S rDNA high-throughput sequencing technology was adopted to compare and analyze the differences in the deep and shallow microflora of birth canal between healthy sows and sows with endometritis，as well as the microflora composition of boar semen.The microflora associated with sow endometritis and the possible effects of boar semen microflora on birth canal microflora of sows were explored.According to the results of microflora analysis，the pathogenic bacteria in the vaginal secretions of sows with endometritis and probiotics in the vaginal secretions of healthy sows were isolated and identified，and the antibacterial effect in vitro<italic/>was tested. <bold>Result</bold> （1）The results of microflora analysis showed that the abundance and coverage of microflora in deep birth canal of healthy sows were significantly higher than that of diseased sows.The dominant bacteria groups in the birth canal of healthy sows were <italic>unclassified_c_Gammaproteobacteria</italic>，<italic>Lactobacillus</italic> and <italic>Corynebacterium</italic>，respectively.The abundance of <italic>Bacteroides</italic>（19.21%），<italic>Porphyromonas</italic>（21.30%）and <italic>Eubacterium nodosus</italic>（1.60%）in the birth canal of diseased sows was significantly higher than that of healthy sows.（2）There was no significant difference between the healthy group and the endometritis group in the shallow part of the birth canal of sows.ASV401，ASV413 and ASV3670 of <italic>Porphyromonas</italic> were detected in the deep and shallow part of the birth canal of infected sows，but not found in the birth canal of healthy sows.（3）In <italic>Salmonella</italic>，ASV5736 was detected only in the deep part of the birth canal of infected sows，but the bacterial community in the deep part of the birth canal of infected sows did not overlap with that of boar semen.（4）One strain of <italic>Proteus mirmiris</italic> was isolated and purified from the deep secretions in the birth canal of diseased sows，and 32 strains of <italic>Lactobacillus</italic> were isolated from the secretions in the birth canal of healthy sows.One strain of <italic>Lactobacillus</italic> salivary was screened out by bacteriostatic test，which had strong bacteriostatic effect on the above <italic>Proteus mirmiris</italic>. <bold>Conclusion</bold> <italic>Bacteroides</italic> and <italic>Porphyromonas</italic> may be the pathogenic bacteria causing endometritis in sows，which is presumed to be caused by the increase of bacteria（groups）in the shallow part of the birth canal of sows，instead of the bacteria community of boar semen.The dominant bacterium in the birth tract of healthy sows was <italic>Lactobacillus</italic>，and a <italic>salivus lactobacillus</italic> with strong antibacterial activity in vitro was successfully screened.The results of this study provided a theoretical basis for exploring the ecological etiology of bacterial sow endometritis and a new direction for the prevention of clinical sow endometritis.