ABSTRACT: The objective of this study was to evaluate the effect of chitosan microparticles on the uterine microbiome of cows with metritis. Dairy cows with metritis (n?=?89) were assigned to 1 of 3 treatments: chitosan microparticles (n?=?21), in which the cows received an intrauterine infusion of chitosan microparticles at metritis diagnosis (day?0), day?2, and day?4; ceftiofur (n?=?25), in which the cows received a subcutaneous injection of ceftiofur on day?0 and day?3; and no intrauterine or subcutaneous treatment (n?=?23). Nonmetritic cows (n?=?20) were healthy cows matched with cows with metritis by the number of days postpartum at metritis diagnosis. Uterine swab samples collected on days?0, 3, 6, 9, and 12 were used for 16S rRNA gene sequencing and 16S RNA gene copy number quantification by quantitative PCR. Principal-coordinate analysis showed that the microbiome of the ceftiofur-treated and metritic untreated groups progressed toward that of the nonmetritic group by day?3, whereas that of the chitosan microparticle-treated group remained unchanged. The differences on day?3 were mainly due to a greater relative abundance of Fusobacteria, particularly Fusobacterium, in the chitosan microparticle-treated group than in the ceftiofur-treated and metritic untreated groups. Furthermore, the microbiome of the ceftiofur-treated group became similar to that of the nonmetritic group by day?9, whereas the microbiome of the chitosan microparticle-treated and metritic untreated groups became similar to that of the nonmetritic group only by day?12. The total bacterial 16S rRNA gene counts in the chitosan microparticle-treated group were greater than those in the metritic untreated controls on days?6 and 9, whereas the ceftiofur treatment group was the only group in which the total bacterial 16S rRNA gene count became similar to that in the nonmetritic group by day?12. In summary, chitosan microparticles slowed the progression of the uterine microbiome toward a healthy state, whereas ceftiofur hastened the progression toward a healthy state.IMPORTANCE Third-generation cephalosporins, such as ceftiofur, are commonly used to treat metritis in dairy cows. Chitosan microparticles has been shown to have a broad spectrum of activity in vitro and to be effective against uterine pathogens in vivo; therefore, they have been hailed as a possible alternative to traditional antibiotics. Nonetheless, in the present study, we saw that chitosan microparticle treatment slowed the progression of the uterine microbiome of cows with metritis toward a healthy state, whereas ceftiofur treatment hastened the progression toward a healthy state. Given the lack of an effective alternative to traditional antibiotics and an increased concern about antimicrobial resistance, a greater effort should be devoted to the prevention of metritis in dairy cows.
