摘要
The linkage between rumen microbiota and feed efficiency has been studied in cattle managed under the drylot system, especially in the feedlot with high-grain diets. However, pasture-based beef operations still dominate the beef production system around the world. In Alberta and other provinces of Canada, most cow-calf producers keep their cattle on summer pasture to lower the labor and feed costs. Similarly, backgrounding beef cattle are mainly operated under the extensive feeding system, mostly on grazing. To date, very limited studies focused on the rumen microbiota of beef cattle under grazing system. To fill this knowledge gap, the present study was performed and is presented in this thesis. This study investigated the interactions of two feeding systems (drylot vs grazing) and feed efficiency (measured with residual feed intake (RFI)) (H-RFI, n=8; L-RFI, n=8) on microbial populations and fermentation products. This study also explored whether the rumen microbiota in heifers with divergent feed efficiency have different change patterns when the feeding system changed. The results showed that the feeding system had significant effects on butyrate and isovalerate concentrations, and acetate to propionate ratio in the rumen. During the transition from drylot to grazing system, heifers with divergent RFI had different patterns of changes in microbial taxonomic compositions. For example, the relative abundance of two predominant phyla Firmicutes and Bacteroidetes were significantly increased and decreased, respectively, only in H-RFI heifers when the feeding system changed from drylot to grazing. These results suggest that these inefficient heifers had more diverse rumen microbial communities than efficient heifers. Rumen microbial functions were also predicted using PICRUSt2 package. In total, 10 major bacterial MetaCyc pathways were predicted, and 7 of them significantly increased only in the rumen of H-RFI heifers when the feeding system changed. This indicates that L-RFI (efficient) heifers have more stable rumen microbiota when the feeding system changed, which also suggests that efficient heifers may maintain their efficiency in different feeding systems through maintaining feed efficiency-related microbes and microbial metabolic pathways. This work provides fundamental knowledge to help to understand the rumen microbiota of cattle under different feeding systems and support the development of potential methods to manipulate rumen microbiota to improve the feed efficiency of beef cattle under grazing.
摘要译文
瘤胃微生物群和饲料效率之间的联系已在干式系统下管理的牛中进行了研究，尤其是在具有高糊化饮食的饲养场中。但是，基于牧场的牛肉业务仍然主导着世界各地的牛肉生产系统。在艾伯塔省和加拿大其他省份，大多数牛排生产商在夏季牧场上保留牛，以降低劳动力和饲料成本。同样，背景牛肉主要在广泛的喂养系统下运营，主要是在放牧下进行的。迄今为止，非常有限的研究集中在放牧系统下的肉牛瘤胃菌群。为了填补这一知识差距，进行了本研究并在本文中介绍。这项研究研究了两个饲养系统（Drylot vs放牧）和饲料效率（用残留饲料摄入量（RFI）（H-RFI，n = 8; L-RFI，n = 8）在微生物种群和发酵产物上的相互作用。这项研究还探讨了饲料效率发散效率的小母牛中的瘤胃微生物群是否具有不同的变化模式。结果表明，饲养系统对丁酸酯和异瓦尔酯浓度产生了重大影响，并且瘤胃中的丙酸乙酸比。在从Dryllot到放牧系统的过渡过程中，具有不同RFI的小母牛具有微生物分类学组成变化的不同模式。例如，仅在喂食系统从干嘴变为放牧时，仅在H-RFI小母牛中显着增加和减少了两个主要的门和细菌群的相对丰度显着增加和减少。这些结果表明，这些效率低下的小母牛的瘤胃微生物群落比有效的小母牛更多样化。还使用PICRUST2软件包预测了瘤胃微生物功能。总共预测了10个主要的细菌Metacyc途径，其中7个仅在喂养系统变化时仅在H-RFI小母牛的瘤胃中显着增加。这表明L-RFI（高效）小母牛在喂养系统发生变化时具有更稳定的瘤胃微生物群，这也表明有效的小母牛通过维持与饲料效率相关的微生物和微生物代谢途径来维持不同喂养系统中的效率。这项工作提供了基本知识，以帮助了解不同饲养系统下牛的瘤胃菌群，并支持开发潜在方法来操纵瘤胃微生物群以提高放牧下的肉牛的饲料效率。
Liu, Junhong. Assessment of rumen microbiota in beef heifers with different feed efficiency and managed under different feeding systems[D]. CA: University of Alberta, 2020