The milk replacer feeding regime in dairy calves has a great impact on metabolic and immunological functioning and affects animal welfare and lifetime performance. The feeding regime influences the rumen microbial composition, and epithelium-associated microbes may interact with the immune system of the host. We examined the correlations between blood leukocyte counts and the rumen epithelium-associated microbiome in dairy calves fed 2 different milk replacer feeding intensities and if these factors related to metabolic traits. Fourteen newborn female dairy calves were allocated to a group receiving either 10% (n = 7) or 20% (n = 7) milk replacer of their body weight (on average 41 kg) and provided ad libitum access to grass hay and concentrate pellets. At 3 weeks of life, all calves were fitted with a rumen cannula. Calves were weaned at 12 weeks of life and received a total mixed ration for ad libitum intake. Pre- (8–10 weeks of life) and post-weaning (21–23 weeks of life), methane production was measured in respiration chambers, and rumen epithelium and blood were sampled for 16S rRNA sequencing and leukocyte analyses, respectively. Pre-weaning, the reduced milk replacer feeding intensity was accompanied with higher concentrate intake but lower growth performance (P < 0.001), a higher abundance of amylolytic and lower abundance of cellulolytic epimural microbes. The group fed a low milk replacer intensity had also greater portions of monocytes (P = 0.031), CD8+ (P < 0.001), and CD14+ (P = 0.044) leukocytes, suggesting elevated inflammatory conditions. Correlations between CD8+ T cells and rumen methanogens, Ruminococcaceae, and Lachnospiraceae were recorded, but these were not consistent throughout maturation. Post-weaning, differences in feed intake and rumen microbial composition converged among milk replacer groups, while differences in growth performance (P = 0.040) and CD8+ cells (P < 0.001) were still present. In conclusion, a reduced milk replacer feeding intensity in dairy calves compromised growth performance and immunity and this effect persisted in the long-term. Significant correlations between the proportion of leukocytes and distinct epimural microbe taxa indicated an interplay between rumen epimural colonization and immune functioning of the host. However, further research is required addressing this interplay between rumen epimural microbes and immune functioning in dairy calves.

中文翻译：

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瘤胃上皮相关微生物群与宿主免疫和代谢适应之间响应奶牛不同代乳品喂养强度的相互作用


奶牛犊的代乳品饲喂制度对代谢和免疫功能有很大影响，并影响动物福利和终生生产性能。摄食方式会影响瘤胃微生物组成，上皮相关微生物可能与宿主的免疫系统相互作用。我们检查了饲喂 2 种不同代乳品喂养强度的奶牛犊的血液白细胞计数与瘤胃上皮相关微生物组之间的相关性，以及这些因素是否与代谢性状相关。将 14 头新生雌性奶牛分配到一组，接受 10% （n = 7） 或 20% （n = 7） 的代乳品（平均 41 公斤），并随意提供草干草和精饲料颗粒。在 3 周出生后，所有犊牛都安装了瘤胃套管。犊牛在 12 周龄时断奶，并接受完全混合日粮以随意采食。在断奶前（8-10 周）和断奶后（21-23 周），在呼吸室中测量甲烷的产生，并分别对瘤胃上皮和血液进行 16S rRNA 测序和白细胞分析。断奶前，代乳品饲喂强度降低，精料摄入量较高，但生长性能较低 （P < 0.001），解淀粉的丰度较高，纤维素溶解壁壁微生物的丰度较低。饲喂低代乳品强度的组也具有更多数量的单核细胞 （P = 0.031）、CD8+ （P < 0.001） 和 CD14+ （P = 0.044） 白细胞，表明炎症状况升高。记录了 CD8 + T 细胞与瘤胃产甲烷菌、瘤胃球菌科和毛螺菌科之间的相关性，但这些在整个成熟过程中并不一致。 断奶后，代乳品组之间采食量和瘤胃微生物组成的差异趋同，而生长性能 （P = 0.040） 和 CD8+ 细胞 （P < 0.001） 的差异仍然存在。总之，奶牛代乳饲喂强度降低会损害生长性能和免疫力，并且这种影响会长期持续存在。白细胞比例与不同的壁壁微生物分类群之间的显著相关性表明瘤胃壁定植与宿主免疫功能之间存在相互作用。然而，需要进一步的研究来解决瘤胃壁壁微生物与奶牛免疫功能之间的这种相互作用。