Abstract
Livestock producers face a number of challenges including pressure from the public to be good environmental stewards and adopt welfare-friendly practices. However, environmental stewardship and animal welfare may have excitingly conflicting objectives. Examples include pasture-based dairy and beef cattle production where high-fiber diets increase methane emissions compared with grain feeding practices in confinement. Livestock account for 35-40% of global anthropogenic emissions of methane, via enteric fermentation and manure, which together account for about 80% of the agricultural emissions. Recent estimates indicate that the methane emissions from African cattle, goats, and sheep are likely to increase from their current level of about 7.8 million tons of methane per year in 2000 to 11.1 million tons per year by 2003, largely driven by increase in livestock numbers. This paper therefore reviews certain areas of CH4 emissions from ruminants, highlights on how some novel feed additives can decrease CH4 emissions from ruminants; and how some plants secondary metabolites might act as a selective inhibitor of methanogens. An enteric methane emission (which is one of the greenhouse gases) represents an economic loss to the farmer where feed is converted to CH4 rather than to product output. As developing countries are now responsible for almost three-quarters of such emissions, this has important implications in terms of mitigation strategies, because these countries are presently outside the remit of the Kyoto Protocol.
Generated Summary
This review article examines the interactions between livestock and the environment, specifically focusing on methane emissions from ruminants. The study highlights the challenges livestock producers face, including pressure from the public to be environmentally responsible. The research reviews the sources of methane emissions in ruminants, the role of methanogens in the process, and potential mitigation strategies. The methodology involves a review of existing literature, focusing on the impact of livestock on greenhouse gas emissions, the role of enteric fermentation and manure, and potential methods to reduce methane production. The scope of the review includes the examination of feed additives, secondary metabolites from plants, and other strategies that could decrease methane emissions. The study aims to provide insights into reducing methane emissions from ruminants to mitigate climate change and promote sustainable livestock practices.
Key Findings & Statistics
- Livestock account for 35-40% of global anthropogenic emissions of methane.
- Enteric fermentation and manure together account for about 80% of agricultural emissions.
- Methane emissions from African cattle, goats, and sheep are estimated to increase from 7.8 million tons per year in 2000 to 11.1 million tons per year by 2030.
- The global warming potential of methane is 21 times that of CO2 over 100 years.
- Methanogenesis corresponds to 2-12% of dietary energy loss.
- Developing countries are responsible for almost three-quarters of enteric methane emissions.
- Methane emission per tropical livestock unit (TLU, 250 kg body weight) varies from 21 kg to 40 kg per year, depending on the production system and diet.
- Sheep and cattle fed diets rich in concentrates contained 107-108 and 108-109 cfu ruminal methanogens/g, respectively.
- High-quality forage can reduce per capita emissions by up to 50%.
- Cattle grazing on mixed alfalfa-grass pasture produce lower emissions per head than those grazing on grass-only pasture.
- Supplementation with whole cottonseed reduces methane emissions.
- The roughage-to-concentrate ratios, as well as the supplementation of soapberry fruit-mango-steen peel pellets containing condensed tannins and saponins, caused changes in ruminal microorganisms, leading to a decrease in methane production.
- Encapsulated fumaric acid decrease methane formation by 76% in the trial with growing lambs.
- The shorter the period of time feed remains in the rumen, the less carbon is converted to methane.
- Dietary encapsulated fumaric acid decrease methane formation by 76% in the trial with growing lambs.
Other Important Findings
- Methane is a significant greenhouse gas, contributing to global warming.
- Enteric methane emissions represent an economic loss to the farmer.
- Methanogenic archaea are key to methane production in the rumen.
- Various feed additives and plant secondary metabolites can reduce methane emissions.
- Different feeding regimes and forage management practices can impact methane production.
- Microbial-intervention strategies have the advantage over improved nutrition strategies in that they do not require a reduction in animal numbers to achieve a reduction in methane emissions.
- Improving metabolic efficiency through the enforced ingestion of growth promoting hormones produces comparable reductions in methane releases.
- High-grain diets can reduce methane emissions and increase animal production efficiency.
- Saponins and tannins have been established to have anti-methanogenic activity.
- Fumarate and malate stimulate hydrogen use for propionate synthesis at the expense of methane in the rumen.
Limitations Noted in the Document
- The effectiveness of different mitigation strategies may vary depending on the production system and diet.
- The long-term effects and sustainability of some mitigation strategies (e.g., feed additives) need further investigation.
- Some of the suggested solutions may have limitations in their practical application on farms.
- The environmental and economic impacts of feed additives and other mitigation methods must be carefully assessed.
- Some strategies may require changes to current agricultural practices.
Conclusion
The review emphasizes the need for sustainable livestock production practices to mitigate methane emissions and address environmental concerns. The study highlights the significant contribution of livestock to global methane emissions and its impact on climate change. The economic implications of enteric methane emissions for farmers are also stressed. The article underscores the importance of developing and implementing effective mitigation strategies, including dietary modifications, feed additives, and improved feeding practices. The review notes that, although various strategies exist, there are limitations in their application. The research suggests that high-grain diets, shorter ruminal fermentation times, and the use of alternative hydrogen acceptors can help reduce methane emissions. Moreover, the review points out the potential of improving production efficiency, modifying rumen bacteria, and the use of plant extracts (such as saponins and tannins) as promising approaches. The study concludes that reducing methane emissions is crucial for both environmental and economic reasons. It also stresses that any livestock production system must consider its environmental impact and implement strategies to minimize it. The manipulation of ruminal fermentation is presented as a key method for improving animal physiology, nutrition, and production, and it is recommended to reduce enteric methane emissions to mitigate global warming.
DOI
10.5897/AJB10.1117