The ideal feed additive should improve diges- tive efficiency while reducing methane emis- sions and main- taining a stable ruminal pH to prevent acidosis.


that reaches the rumen while the animals are feeding. Anaer- obic microbial species include prokaryotes, such as bacteria or archaea, and eukaryotes, such as protozoa, fungi and virus- es. The most common micro-organisms in the rumen are bac- teria, which account for 95% of the microbial species, while prokaryotes represent a large proportion of the microbial bio- mass due to their cell volume. Firmicutes, Bacteroidetes and Proteobacteria have been described as the most abundant bacterial species found in the rumen microbiome and the ra- tio between Firmicutes and Bacteroidetes can influence the efficiency of ruminants. It has been reported that an increase in the Firmicutes: Bacteroidetes ratio is associated with an in- crease in average daily gain and a reduction in feed intake. Fi- brobacter, Ruminococcus, Butyvibrio and Bacteroidetes are all fibre-degrading microbes that are commonly found in ru- minants; however, other bacteria such as Prevotella, Strepto- coccus, Lactobacillus and Megasphaera are also present. Methane-producing microbes, anaerobic fungi and ciliate protozoa likewise form part of the rumen microbiome popu- lation. The large variation in microbial species is due to the supply of dietary components from feed and the continuous removal of fermentation end products such as VFAs and methane. Even though nutrition has the biggest influence on the rumen microbiome, the core rumen microbiome is also influenced by the genetic composition of the host.


24 ▶ ALL ABOUT FEED | Volume 28, No. 6, 2020


The efficiency of the microbiome If you can increase the efficiency of the rumen microbiome through the manipulation of microbial fermentation, produc- tion efficiency will also be increased. Many microbiome stud- ies link traditional feed efficiency measurements such as feed conversion ratio, average daily gain, feed intake and residual feed intake to the microbiome composition of the animals. Metagenomics can be used to analyse the rumen microbial community to identify indicators that show variations in aver- age daily gain and feed intake as measurements of feed effi- ciency. These feed efficiency measurements, which are linked to specific microbes, can then be used to improve the genetic selection of animals to further improve breeding for higher production and efficiency. Strategies such as the use of feed additives can be developed to increase the abundance of beneficial microbes within the rumen microbiome. The iden- tification of rumen microbial species can thus be used to pre- dict an animal’s feed efficiency. Researchers have found that efficient animals had a higher abundance of Succiniclasticum, which specialises in the fermentation of succinate to propion- ate. Propionate-producing bacteria use hydrogen, a by-prod- uct of the fermentation process, to produce propionate, re- sulting in an increase in the energy available to the animal. Studies have shown that an increased propionate:acetate ra- tio is found in efficient animals. Variation in feed efficiency


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