Abundances of rumen microbial genes can help predict cattle’s appetite and growth

14 Apr 2020

Researchers in the Leading Host Genetics and Microbiome Research group at the Scottish Rural College and University of Edinburgh found that abundances of specific rumen microbial genes of were closely associated to the appetite and growth of beef cattle. This project is being undertaken by PhD student Joana Lima, supervised by Professor Rainer Roehe.

Ruminants are interesting because they feed on plant materials that would be indigestible for humans and convert them into nutritious food products for human consumption such as meat and milk. Mammals, including cattle, do not produce the necessary enzymes to digest the plant biomass they ingest. However, ruminants live in a symbiotic relationship with the rumen microbiota – the whole collection of microbes (bacteria, archaea, protozoa and fungi) that inhabits the rumen. These microbes can break down the plant materials ingested by the host animal. During this process, they release fatty acids (energy), and produce bacterial proteins the animal can absorb or digest to be used for its own growth. This way, microbes influence cattle digestion, and can influence the animals’ appetite and growth.

Since each microbial species is characterised by a different set of genes, researchers can either focus on what microbe species are present in the rumen (microbiota) or on the whole collection of DNA present in these organisms (microbial genes). The study of both these perspectives can clarify the role of the rumen microbes in the digestion process. If researchers are focused on the microbial species they can understand, for example, which microbial species are more abundant in animals with higher growth rate. On the other hand, given that each gene is associated with a single protein, focusing on the functional genes of these microbes can be useful to understand why a certain species is associated to a host trait, such as appetite. This project was focused on the identification of microbial genes associated with appetite and weight gain in beef cattle. Additionally, it also highlighted which microbial functions within the rumen could be having an impact on these host traits.

This study uses 42 steers from four different breeds (Luing and crossbreeds Charolais, Limousin and Aberdeen Angus). These cattle were fed one of two different basal diets (forage and concentrate). The animals were measured for their daily feed intake (i.e. appetite) and average daily weight gain. Samples from rumen digesta from these cattle were obtained at the abattoir. The individual abundances of 1135 microbial genes were determined from the rumen digesta samples.

This study showed that the abundances of 14 and 18 rumen microbial genes explained 65% and 73% of the variation observed in appetite and weight gain, respectively. Although the sets of microbial genes identified here were different, both included functions related to break-down and digestion of feed and host-microbiome communication. This includes carbohydrates and amino-acids metabolism, and resistance to the host. These results underline the importance of the rumen microbiome in feed conversion processes. In the future, this kind of results could be incorporated into programs for selection of breeding animals.

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