Livestock production and climate change.

Chapter 8 (Page no: 111)

Perspective on livestock-generated GHGs and climate.

The greenhouse gases (GHGs) attributed to agriculture and animal agriculture are methane (CH₄) and nitrous oxide (N₂O). The relative absorptivity of the infrared radiation of carbon dioxide (CO₂) is about 21-fold and 310-fold higher than for each molecule of CH₄ or N₂O, respectively. As the absorptivity in both gases is not saturated like CO₂, the contribution of CH₄ and N₂O to the greenhouse effect have therefore been prospectively increasing linearly, because atmospheric increases in the concentration of both gases correlate closely with human activities, and the world population is currently expanding to more than 7 billion. Rumen CH₄ production emitted to the atmosphere can be accounted as the biggest anthropogenic source. The abatement mechanism of rumen CH₄ emission may be divided into direct and indirect suppression of methanogens in the rumen. The most significant strategy to mitigate rumen CH₄ emission in an indirect manner is to promote alternative metabolic pathways to dispose of the reducing power, competing with methanogenesis for H₂ uptake. In an attempt to identify natural manipulators with the efficacy to mitigate rumen CH₄ emission, efficient prebiotics and probiotics have been developed in various institutions instead of ionophores in respect to food safety. The relatively lower molecular weight compounds produced by Lactobacillus plantarum have recently revealed the ability to suppress rumen methanogenesis. Some tropical and subtropical legume trees fed to cattle and buffalo as a protein source, due to their high protein content, are rich in secondary metabolites such as saponin and tannin, which is a type of polyphenol, etc. Some of them have been reported to abate rumen CH₄ production remarkably well in vitro or in vivo. In some cases, however, experimental results are in agreement but may not match. Meta-analysis might be useful to integrate statistically the experimental results from independent studies for comprehensive understanding in the next stage of research. Although the inventory assessment of N₂O is still ongoing, animal manures, including those from monogastrics, have been listed as a significant contributor. The incomprehensible fates of organic and inorganic nitrogen compounds contained in the aerobic composting of animal manures may confuse an accurate evaluation of the actual emission of N₂O from animal manures. Of late, there has been an urgent need for renewable energy production using anaerobic digesters to capture biogas (CH₄) from animal effluent. Most manure nitrogen during fermentation has been converted to an inorganic form in the digested slurry.

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