Methane mitigation in dairy cows

Global greenhouse gas (GHG) emissions include carbon dioxide (CO2), methane (CH4) and nitrous oxide (NO2). Agricultural emissions contribute to 40% of the total methane from anthropogenic sources of which 25% arise from enteric fermentation in livestock mainly ruminants. Dairy cows emit high levels of methane (CH4) which is a major source of greenhouse gas and therefore possesses detrimental effects to the environment. Moreover methane results in energy loss for ruminants which is assumed to vary between 2 % to 12 % of gross energy intake. Therefore, measures to mitigate enteric CH4 formation from dairy cows will be undertaken in this project without altering animal production as a strategy to reduce the global GHG emissions and for improving the sustainability of dairy production.

The rumen is a complex eco-system consisting of various symbiotic anaerobic micro-organisms such as bacteria, archaea, ciliated protozoa and fungi. Methane is produced predominantly in the rumen (fore-stomach) of the dairy cow (87%) and to a small extent in the small intestine (13%). These regions are the source of active microbial breakdown of dietary plant cell wall polysaccharides. The herbivorous diet consists primarily of plant cell wall polysaccharides that is built up of cellulose, hemi-cellulose, starch, pectin, mono- and di-saccharides. Typically, these compounds cannot be digested by host enzymes, and 70% of the total gut volume is typically devoted to microbial fermentation (Figure 1).

Figure 1 Microbial methanogenic degradation of plant fibres in dairy cow.
Figure 1 Microbial methanogenic degradation of plant fibres in dairy cow.

The polysaccharides from the feed initially undergo hydrolysis, resulting in the release of the respective monomers ( for example hexoses). Fermentation of these monomers (Acidogenesis , Fig 1) in the rumen of the dairy cow results in the production of a variety of organic and short chain fatty acids (SCFA’s) along with hydrogen and carbon dioxide. The H2 and CO2 formed are further used by the methanogenic archaea to produce methane. In contrast,  the SCFA’s produced during feed fermentation are used by the micro-organisms, as the soluble forms  are absorbed in the blood stream and used by the host as  energy source. In addition, formate and Hydrogen CO2 and acetate, formed in the acetogenic phase, are used as a substrate for methanogenesis,. To understand digestion and methane formation in the rumen, it is important to understand the physiology and ecology of methanogens, e.g. with different diets and/or ruminant genotypes. This can help elucidate the role of methanogenesis in the rumen and the mechanisms of this process. In addition, a complex community of micro-organisms is involved in the degradation of fibre in the rumen. As the fundamental purpose of the rumen is to breakdown complex material, the importance of maximising the process of fibre degradation is obvious.

Specific objectives of this study will be:

  1. To identify microbial biomarkers that are indicative for methane emission.
  2. To construct “a metabolic map” for rumen metabolism
  3. To define and establish mixed populations reflecting the metabolic map in the rumen
  4. To identify the microbial populations specifically involved in the initial fibre degradatio

This project is part of the research project “Methane reduction in dairy cows” of the Top Institute Food and Nutrition (TIFN).