Park Tansol, Ma Lu, Gao Shengtao, Bu Dengpan, Yu Zhongtang
Department of Animal Sciences, The Ohio State University, Columbus, OH, USA.
Department of Animal Science and Technology, Chung-Ang University, Anseong-si, Gyeonggi-do, Republic of Korea.
J Anim Sci Biotechnol. 2022 Jun 15;13(1):71. doi: 10.1186/s40104-022-00717-z.
Heat stress (HS) affects the ruminal microbiota and decreases the lactation performance of dairy cows. Because HS decreases feed intake, the results of previous studies were confounded by the effect of HS on feed intake. This study examined the direct effect of HS on the ruminal microbiota using lactating Holstein cows that were pair-fed and housed in environmental chambers in a 2 × 2 crossover design. The cows were pair-fed the same amount of identical total mixed ration to eliminate the effect of feed or feed intake. The composition and structure of the microbiota of prokaryotes, fungi, and protozoa were analyzed using metataxonomics and compared between two thermal conditions: pair-fed thermoneutrality (PFTN, thermal humidity index: 65.5) and HS (87.2 for daytime and 81.8 for nighttime).
The HS conditions altered the structure of the prokaryotic microbiota and the protozoal microbiota, but not the fungal microbiota. Heat stress significantly increased the relative abundance of Bacteroidetes (primarily Gram-negative bacteria) while decreasing that of Firmicutes (primarily Gram-positive bacteria) and the Firmicutes-to-Bacteroidetes ratio. Some genera were exclusively found in the heat-stressed cows and thermal control cows. Some co-occurrence and mutual exclusion between some genera were also found exclusively for each thermal condition. Heat stress did not significantly affect the overall functional features predicted using the 16S rRNA gene sequences and ITS1 sequences, but some enzyme-coding genes altered their relative abundance in response to HS.
Overall, HS affected the prokaryotes, fungi, and protozoa of the ruminal microbiota in lactating Holstein cows to a different extent, but the effect on the structure of ruminal microbiota and functional profiles was limited when not confounded by the effect on feed intake. However, some genera and co-occurrence were exclusively found in the rumen of heat-stressed cows. These effects should be attributed to the direct effect of heat stress on the host metabolism, physiology, and behavior. Some of the "heat-stress resistant" microbes may be useful as potential probiotics for cows under heat stress.
热应激（HS）会影响瘤胃微生物群，并降低奶牛的泌乳性能。由于热应激会减少采食量，先前研究的结果受到热应激对采食量影响的干扰。本研究采用2×2交叉设计，对泌乳期荷斯坦奶牛进行配对饲养，并将其安置在环境舱中，以研究热应激对瘤胃微生物群的直接影响。给奶牛配对投喂等量的相同全混合日粮，以消除饲料或采食量的影响。使用宏分类学分析原核生物、真菌和原生动物微生物群的组成和结构，并在两种热条件下进行比较：配对饲养的中性温度（PFTN，热湿指数：65.5）和热应激（白天87.2，夜间81.8）。
热应激条件改变了原核生物微生物群和原生动物微生物群的结构，但未改变真菌微生物群的结构。热应激显著增加了拟杆菌门（主要是革兰氏阴性菌）的相对丰度，同时降低了厚壁菌门（主要是革兰氏阳性菌）的相对丰度以及厚壁菌门与拟杆菌门的比例。一些属仅在热应激奶牛和热对照奶牛中被发现。在每种热条件下还分别发现了一些属之间的共现和互斥关系。热应激对使用16S rRNA基因序列和ITS1序列预测的整体功能特征没有显著影响，但一些酶编码基因的相对丰度因热应激而发生了改变。
总体而言，热应激对泌乳期荷斯坦奶牛瘤胃微生物群中的原核生物、真菌和原生动物有不同程度的影响，但在不受采食量影响时，对瘤胃微生物群结构和功能谱的影响有限。然而，一些属和共现关系仅在热应激奶牛的瘤胃中被发现。这些影响应归因于热应激对宿主代谢、生理和行为的直接作用。一些“耐热应激”微生物可能作为热应激奶牛的潜在益生菌具有应用价值。
