July 01, 2018

Interpretive Summary: Poor feed efficiency in sheep is associated with several structural abnormalities in the community metabolic network of their ruminal microbes

Interpretive Summary: Poor feed efficiency in sheep is associated with several structural abnormalities in the community metabolic network of their ruminal microbes.

By: Surely Wallace

In a June 2018 article published in the Journal of Animal Science, researchers investigated the relationship between feed efficiency in sheep and their ruminal microbiomes. The authors point out there has historically been a great deal of difficulty in characterizing this link because multiple factors (e.g. diet, host genes, environment) in addition to microbial community function may be more indicative of effect on feed efficiency, than simple microbial taxonomy. Therefore, the authors chose to focus on the hypothesis that function of the microbial ecosystem would be a better indicator to potentially characterize differences in sheep feed efficiency.

Symbiosis between rumen animals and their microbes is critically important in animal nutrition, with rumen microbes breaking down otherwise indigestible complex polysaccharides into more digestible forms for utilization by the host animal. Better understanding how rumen microbes may potentially affect feed efficiency would therefore be useful for both economic and environmental reasons. There are a limited number of studies looking for potential links between rumen feed efficiency and the functional qualities of the rumen microbiome, however. 

In this study, a total of 16 Targhee ewes (8 with very high residual feed intake (RFI) and 8 with very low RFI) were selected. A Tygon tube was used to extract rumen fluid of 30 mL or greater volume from each animal. Microbial DNA was then extracted from the fluid and sequenced with Illumina 16S HiSeq 2500. The authors constructed a metabolic network using the MetaCyc database for microbes, and from known human and cattle orthologs for the sheep host genome.

A microbial metabolic network map was created in order to link microbe populations with potential function (metabolites produced). The goal was to compare the functional microbial profiles of low (efficient) and high (inefficient) RFI animals to determine if differences in these profiles could potentially explain extremes in animal feed efficiency. The authors did not find any causal links, however, they reported the following trends: low RFI sheep had microbiomes with metabolic networks that produced enzymes that were similar in function to host reactions, with these reactions also involving shorter carbon chain molecules. Additionally, low RFI sheep had a higher Shannon diversity index, suggesting a greater diversity of their rumen microbiome. 

The authors stress that there is a great deal of difficulty in characterizing any causal relationships between feed efficiency and rumen microbiome due to the complex nature of host-microbe interactions, which are often not direct or linear. The association of low RFI sheep with increased Shannon diversity index in this study, however, does suggest there may be a need to better examine the potential effects of antibiotics on sheep microbial diversity and feed efficiency. Overall, more in-depth studies characterizing the function of rumen microbial ecosystems via a systems approach is warranted.

To view the full article, “Poor feed efficiency in sheep is associated with several structural abnormalities in the community metabolic network of their ruminal microbes,” visit the Journal of Animal Science.