It is generally accepted that postpartum uterine infections decrease conception rates in dairy cows. Whereas clinical endometritis (CE) has been studied intensively, only little information about CE at the time of artificial insemination (AI) is available. The aim of this study was to characterize the intrauterine cultivable aerobic microbiota in healthy cows and in cows with mild CE at AI and to investigate its effect on the subsequent insemination success. The vaginal discharge score (VDS) of 120 Holstein Frisian dairy cows was assessed shortly after AI using the Metricheck device and pregnancy diagnosis was performed 39 days after AI. On average, cows received their second insemination (2.0 ± 1.2 standard deviation (SD)) and were 120.5 ± 40.2 days in milk. Intrauterine cytobrush samples were taken from cows with clear mucus (VDS 0, n = 58) and from cows with flecks of pus (VDS 1, n = 62), which was regarded as mild CE. Bacteria collected with the cytobrush were cultivated aerobically and identified by matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). A total of 358 bacterial isolates were recovered, comprising 49 bacterial genera and 116 species. Bacillus, Staphylococcus, Corynebacterium and Streptococcus were the most prevalent genera with relative abundances of 19.6%, 14.2%, 10.1% and 8.1%, whereas common uterine pathogens, such as Trueperella pyogenes and Escherichia coli, were rarely detected. Bacillus spp. were more frequently detected in group VDS 0 (51.7%) than in VDS 1 (22.6%; P = 0.001) and there was a higher prevalence of Corynebacterium spp. in VDS 0 than in VDS 1 (37.9% vs 19.3%; P = 0.03). Cows with VDS 1 at the time of AI harbored neither Bacillus licheniformis nor Bacillus subtilis, while these species were detected in 27.6% and 8.6% of VDS 0 (P < 0.001 and P = 0.024 respectively). The insemination success in VDS 0 and 1 was 43.1 and 25.8% (P = 0.046). The diagnosis of mild CE at AI and the total bacterial load decreased the chance of pregnancy (P = 0.03) but no significant correlation between a distinctive bacterial species and insemination success was observed. In summary, cultivable uterine bacteria at AI presumably represent a part of the physiological microbiota, which is not directly linked to impaired fertility. These findings question intrauterine antimicrobial treatment shortly after AI and could represent the basis for the development of future treatment strategies.

中文翻译：

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轻度子宫内膜炎和非轻度子宫内膜炎奶牛授精时宫内可培养需氧菌群的特征

人们普遍认为产后子宫感染会降低奶牛的受孕率。尽管对临床子宫内膜炎 (CE) 进行了深入研究，但关于人工授精 (AI) 时 CE 的信息很少。本研究的目的是表征健康奶牛和 AI 轻度 CE 奶牛的宫内可培养需氧微生物群，并研究其对后续授精成功的影响。使用 Metricheck 设备在人工授精后不久评估 120 头荷斯坦弗里斯兰奶牛的阴道分泌物评分 (VDS)，并在人工授精后 39 天进行妊娠诊断。平均而言，奶牛接受了第二次授精（2.0 ± 1.2 标准差 (SD)），并且在牛奶中待了 120.5 ± 40.2 天。宫内细胞刷样本取自具有透明粘液 (VDS 0, n = 58) 和带有脓液斑点的奶牛 (VDS 1, n = 62)，被认为是轻度 CE。用细胞刷收集的细菌有氧培养，并通过基质辅助激光解吸电离飞行时间质谱 (MALDI-TOF MS) 进行鉴定。共回收细菌分离株358株，包括49个细菌属和116个种。芽孢杆菌、葡萄球菌、棒状杆菌和链球菌是最普遍的属，相对丰度分别为 19.6%、14.2%、10.1% 和 8.1%，而常见的子宫病原体，如化脓性真肠菌和大肠杆菌，很少检测到。芽孢杆菌属 VDS 0 组 (51.7%) 比 VDS 1 组 (22.6%; P = 0.001) 更频繁地检测到，并且棒状杆菌属的患病率更高。在 VDS 0 中比在 VDS 1 中（37.9% 对 19.3%；P = 0.03）。在 AI 时具有 VDS 1 的奶牛既没有地衣芽孢杆菌也没有枯草芽孢杆菌，而在 VDS 0 的 27.6% 和 8.6% 中检测到这些物种（分别为 P < 0.001 和 P = 0.024）。VDS 0 和 1 的授精成功率为 43.1% 和 25.8% (P = 0.046)。AI 时轻度 CE 的诊断和总细菌载量降低了怀孕的机会 (P = 0.03)，但未观察到独特的细菌种类与授精成功之间的显着相关性。总之，在 AI 可培养的子宫细菌可能代表了生理微生物群的一部分，这与生育能力受损没有直接关系。这些发现对 AI 后不久的宫内抗生素治疗提出质疑，并可能代表未来治疗策略的发展基础。