Abstract
A better understanding of global ruminal microbiota and metabolites under extensive feeding conditions is a prerequisite for optimizing rumen function and improving ruminant feed efficiency. Furthermore, the gap between the information on the ruminal microbiota and metabolites needs to be bridged. The aim of this study was to investigate the effects of a wide range of forage to concentrate ratios (F:C) on changes and interactions of ruminal microbiota and metabolites. Four diets with different F:C (80:20, 60:40, 40:60, and 20:80) were limit-fed to 24 Holstein heifers, and Illumina MiSeq sequencing and gas chromatography time-of-flight/mass spectrometry were used to investigate the profile changes of the ruminal microbes and metabolites, and the interaction between them. The predominant bacterial phyla in the rumen were Bacteroidetes (57.2 ± 2.6%) and Firmicutes (26.8 ± 1.6%), and the predominant anaerobic fungi were Neocallimastigomycota (64.3 ± 3.8%) and Ascomycota (22.6 ± 2.4%). In total, 44, 9, 25, and 2 genera, respectively, were identified as the core rumen bacteria, ciliate protozoa, anaerobic fungi, and archaea communities across all samples. An increased concentrate level linearly decreased the relative abundance of cellulolytic bacteria and ciliates, namely Fibrobacter, Succinimonas, Polyplastron, and Ostracodinium (q < 0.05), and linearly increased the relative abundance of Entodinium (q = 0.04), which is a non-fibrous carbohydrate degrader. Dietary F:C had no effect on the communities of anaerobic fungi and archaea. Rumen metabolomics analysis revealed that ruminal amino acids, lipids, organic acids, and carbohydrates were altered significantly by altering the dietary F:C. With increasing dietary concentrate levels, the proportions of propionate and butyrate linearly increased in the rumen (P ≤ 0.01). Correlation analysis revealed that there was some utilization relationship or productive association between candidate metabolites and affected microbe groups. This study provides a better understanding of ruminal microbiota and metabolites under a wide range of dietary F:C, which could further reveal integrative information of rumen function and lead to an improvement in ruminant production.
Highlights
The rumen is a complex microbial ecosystem and is inhabited by a high density of resident microbiota, with bacteria, ciliate protozoa, anaerobic fungi, and archaea involved (Hobson and Stewart, 1997)
Rumen microorganisms play important roles in the degradation of feedstuffs and the production of volatile fatty acids (VFAs), lactate, amino acids, lipids, and hydrogen, which are crucial to the maintenance, growth, and production performance of ruminants (Shabat et al, 2016)
When a high level of concentrate is used in diets in a sudden change, dairy cows are at a high risk of suffering from subacute ruminal acidosis (SARA), which results in a high risk of chronic inflammation, lameness, mastitis, and laminitis (Zebeli and Metzler-Zebeli, 2012; Mao et al, 2016; Hua et al, 2017)
Summary
The rumen is a complex microbial ecosystem and is inhabited by a high density of resident microbiota, with bacteria, ciliate protozoa, anaerobic fungi, and archaea involved (Hobson and Stewart, 1997). Due to the complexity of the rumen ecosystem, a better understanding of the ruminal microbiota under extensive feeding conditions is a necessary prerequisite for the manipulation of the rumen microbiota to optimize rumen function and improve feed efficiency (Jami and Mizrahi, 2012; Bannink et al, 2016). Limit-feeding dairy heifers with high-concentrate diets was proposed as a potential strategy to improve feed efficiency in dairy farms (Zanton and Heinrichs, 2007, 2009, 2016) and can serve as an excellent model for examining the effects of a wide range of F:C on the ruminal microbiota. The importance of the microbiota in the rumen function has been recognized for decades; the dynamic changes of the ruminal microbiota and metabolic profiles in animals limit-fed high-concentrate diets remain unclear
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
