Abstract
The relationship between rumen microbiota and host feed efficiency phenotype, for genetically divergent beef cattle breeds is unclear. This is further exacerbated when different growth stages, chemically diverse diets and production systems are considered. Residual feed intake (RFI), a measure of feed efficiency, was calculated for individually fed Charolais (CH) and Holstein–Friesian (HF) steers during each of four 70-day (excluding adaptation) successive dietary phases: namely, high-concentrate, grass silage, fresh zero-grazed grass and high-concentrate again. Rumen fluid from the ten highest- (HRFI) and ten lowest-ranking (LRFI) animals for RFI, within breed, during each dietary phase was collected using a trans-oesophageal sampler and subjected to 16S rRNA amplicon sequencing and metabolic profiling. The datasets were analysed to identify microbial and rumen fermentation markers associated with RFI status. Age, dietary phase and breed were included in the statistical model. Within breed, for each dietary phase, mid-test metabolic weight and average daily gain did not differ (P > 0.05) between HRFI and LRFI steers; however, for the initial high-concentrate, grass silage, fresh grass herbage and final high-concentrate dietary phases, HRFI HF steers consumed 19, 23, 18 and 27% more (P < 0.001) than their LRFI counterparts. Corresponding percentages for CH HRFI compared to CH LRFI steers were 18, 23, 13 and 22%. Ten OTUs were associated with RFI (q < 0.05) independent of the other factors investigated. Of these Methanomassiliicoccaceae, Mogibacteriaceae and the genus p-75-a5 of Erysipelotrichaceae and were negatively associated (q < 0.05) with RFI. The results gave evidence that microbial species could potentially be an indicator of RFI in ruminants rather than broader microbiome metrics; however, further research is required to elucidate this association.
Highlights
The relationship between rumen microbiota and host feed efficiency phenotype, for genetically divergent beef cattle breeds is unclear
For high-concentrate, grass silage, fresh grass herbage and high-concentrate dietary phases, high RFI (HRFI) HF steers consumed 19, 23, 18, and 27% more (P < 0.001) than their low Residual feed intake (RFI) counterparts, respectively (Table 1)
There have been some reports of differences in overall community structure in relation to RFI14,31, research from this study indicates that it is more likely that individual microbial species or strains may impact the efficiency of the animal more than an overall ruminal community shift
Summary
The relationship between rumen microbiota and host feed efficiency phenotype, for genetically divergent beef cattle breeds is unclear. Et al.[8] and Coyle et al.[22] have demonstrated that RFI phenotype is moderately repeatable for cattle offered the same diet over different phases of their lifetime; repeatability is reduced when contrasting diets are fed successively (i.e. forage versus concentrate-based diets), as per commercial farming p ractice[23] These results may have implications for beef genetic evaluations and breeding programmes. The current study investigated the effect of RFI phenotype of both beef and dairy bred steers across common dietary phases of Irish pastoral-based beef production systems on the rumen microbiome and its metabolites This aims to elucidate if particular microbial taxa influence host FE phenotype independent of stage of production, diet and host breed, leading to the potential for rumen microbiome manipulation or selection for FE based on microbial markers
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