Ruminats and sustainable nutrition: tannin molecules impacts on methane emissions

Climate change poses numerous challenges for the world, such as the sustainable use of natural resources and the reduction of greenhouse gases emissions. In this context, the livestock sector must face the high global demand for animal-source products by increasing its sustainability. Livestock production is the source of animal proteins, which are essential for human nutrition. Among all the livestock species, ruminants play a major role. Ruminants are herbivorous animals and their diet is mainly composed of plant fibers. Plant fibers are usually characterized by poor quality and are indigestible for humans. Thanks to the fermentation processes occurring in the rumen, ruminants can convert and upgrade this low-quality biomass into energy and high-quality animal proteins. The processes occurring in rumen are named enteric fermentation and are exerted by the rumen microbial community. The rumen microbiota is composed of bacteria, protozoa, archea, and fungi that can ferment the polysaccharides of the plant fibers, producing volatile fatty acids (the main energy source for ruminants) and gases such as hydrogen and carbon dioxide. However, during the enteric fermentation, there are several bacteria that produce methane, in order to balance the hydrogen pressure in the rumen. This is one element responsible for the environmental footprint of ruminant production. The application of strategies aimed at reducing methane emissions from ruminants is therefore crucial to make ruminant nutrition more sustainable, while maintaining animal health and productive performance. The dietary supplementation with tannins is known to reduce the environmental impact of ruminants by decreasing the rate of methane production. Indeed, tannins can affect the metabolic activity of the methanogen bacteria, thus reducing the production of methane by the enteric fermentation. However, the use of tannins can also show some detrimental effects in terms of feed digestibility and feed intake. We decided to investigate this topic by applying in vitro models to assess the effect of two tannin molecules, named ellagic acid and gallic acid, on rumen fermentation and in particular on methane emissions. The in vitro models of rumen fermentation are an efficient way to set up the experimental plan and to standardize the experimental conditions before moving to the in vivo condition. The research project led to promising results about the mitigation of methane emissions, but further research is needed to clear the activity of tannins on the rumen microbial community. This research project was supported by the University of Milan and two research institutes in Switzerland: Agroscope (Posieux) and AgroVet-Strickhof (Lindau). This work was presented in two international scientific congresses: 1) 75° SISVET congress (15-18 June 2022, Lodi, IT); 73° EAAP congress (5-9 September 2022, Porto, PT).