MANAGING FARMS FOR ENVIRONMENTAL STEWARDSHIP AND PROFIT
Location: Pasture Systems & Watershed Management Research
Title: Mitigation of greenhouse gas emissions in livestock production: a review of technical options for non-C02 emissions
| Hristov, Alexander - |
| Oh, Joonpyo - |
| Lee, Chanhee - |
| Meinen, Robert - |
| Montes, Felipe - |
| Ott, Troy - |
| Firkins, Jeff - |
| Adesogan, Adegbola - |
| Yang, Wenzhu - |
| Tricarico, Juan - |
| Kebreab, Ermias - |
| Waghorn, Gary - |
| Dijkstra, Jan - |
| Oosting, Simon - |
Submitted to: Food and Agriculture Organization of the United Nations Technical Workshop Report
Publication Type: Other
Publication Acceptance Date: June 12, 2012
Publication Date: January 15, 2013
Citation: Hristov, A.N., Oh, J., Lee, C., Meinen, R., Montes, F., Ott, T., Firkins, J., Rotz, C.A., Dell, C.J., Adesogan, A., Yang, W., Tricarico, J., Kebreab, E., Waghorn, G., Dijkstra, J., Oosting, S. 2013. Mitigation of greenhouse gas emissions in livestock production: a review of technical options for non-C02 emissions. Food and Agriculture Organization of the United Nations Technical Workshop Report. p 1-255.
Interpretive Summary: An interpretive summary is not required.
Animal production is a significant source of greenhouse gas (GHG) emissions worldwide. This analysis was done to evaluate the potential use of nutritional, manure, and animal management practices to mitigate non-CO2 GHG emissions (i.e., methane, CH4 and nitrous oxide, N2O) from enteric fermentation and manure decomposition. Mitigation practices were categorized as enteric CH4 mitigation practices, dietary management and N2O emissions from manure, manure management mitigation practices, and animal management mitigation practices.
Nitrates show promise as enteric CH4 mitigation agents, particularly in low-protein diets that can benefit from nitrogen supplementation, but more in vivo studies are needed to fully understand their impact on whole-farm GHG emissions, animal production, and animal health. Ionophores, through their effect on feed efficiency, likely have a moderate CH4 mitigating effect in ruminants fed grain-forage diets. In ruminants fed pasture, the effect of ionophores is not sufficiently consistent to be adopted as a mitigation strategy. Hydrolysable tannins may reduce enteric CH4 production, although intake and milk production may be compromised. Vaccines against rumen archaea offer an exciting mitigation opportunity for the future, but the extent of CH4 reduction appears small and persistence of the effect is unknown. Dietary oils are effective in reducing enteric CH4 emission, but the feasibility of this mitigation practice will depend on its cost-effectiveness and the mitigation potential must be expressed per unit of product (and milk components with dairy production systems) to account for potential negative impacts on feed intake, production, or milk composition. Inclusion of concentrate feeds in the diet of ruminants will likely decrease enteric CH4 emission per unit of product, particularly when inclusion is above 35 to 40% of dry matter intake, but the effect will depend on inclusion level, production response, effect on fiber digestibility, plane of nutrition, feed type, feed processing, and likely animal species. In many parts of the world, this also may not be economically feasible. Increased forage digestibility is expected to increase production and decrease eneteric CH4 production per unit of product. It appears that the introduction of legumes in warm climate regions offers a mitigation opportunity. Forage with higher sugar content (high-sugar grasses or harvested in the afternoon) may reduce urinary nitrogen losses and consequently N2O emission from manure applied to soil, although more research is needed to support this concept. Increasing forage digestibility, intake, and animal production reduces overall GHG emission from rumen fermentation and stored manure and are highly-recommended mitigation practices. Processing of grain to increase its digestibility likely reduces enteric CH4 production per unit of animal product, but caution should be exercised that fiber digestibility is not decreased. This mitigation practice may not be economically feasible in many developing countries, but minimal processing is highly recommended so grain energy is better utilized for animal production. Improving the nutritive value of low quality feeds in ruminant diets can have a considerable benefit on herd productivity while keeping the herd CH4 output constant. Consequentially, CH4 emission per unit of product is reduced. Chemical treatment of low quality feeds, supplementation, breeding, and selection for straw quality are easily applied, but there has been little adoption of these technologies on farms. Feeding protein close to animal requirements, including varying protein concentration with stage of lactation or growth, is recommended as an effective manure ammonia and N2O emission mitigation practice. Low-protein diets for ruminants should be balanced for rumen-degraded protein so microbial protein synthesis and fiber degradability are not impaired. Diets for all animals should be balanced to meet amino acid requirements to avoid feed intake depression and decreased production.
Diet can have a significant impact on manure GHG emissions during storage and following land application. Decreased digestibility of dietary nutrients is expected to increase fermentable organic matter concentration in manure, which may increase manure CH4 emission. Restricting grazing when conditions are most favorable for N2O formation, more uniform distribution of urine, and optimizing fertilizer application are possible N2O mitigation options for ruminants on pasture. Urease and nitrification inhibitors are promising treatments to reduce N2O emissions from intensive livestock production systems, but they are costly and result in limited benefit to the producer. Most mitigation options for GHG emissions from stored manure, such as reducing the time of manure storage, aeration, slatted floors, and stacking are generally aimed at decreasing the time allowed for microbial fermentation processes to occur before land application. These mitigation practices are effective, but their economic feasibility is uncertain. Semi-permeable covers are useful for reducing ammonia, CH4, and odor emissions, but likely increase N2O emissions. Impermeable membranes, such as oil layers and sealed plastic covers are effective in reducing gaseous emissions, but are not very practical. Combusting the CH4 that accumulates under impermeable covers to produce electricity or heat is recommended. Anaerobic digesters are a recommended mitigation strategy for CH4. Management of digestion systems is important to assure they do not become net emitters of GHG. These systems require large initial capital investments, and as a result, their adoption may occur only when economic incentives are offered. Lowering the nitrogen concentration in manure, preventing anaerobic conditions, and reducing the input of degradable manure carbon are successful strategies for reducing GHG emissions from manure applied to soil. Separation of manure solids and anaerobic degradation pretreatments can mitigate CH4 emission from subsurface-applied manure, which may otherwise be greater than that from surface-applied manure. Timing of manure application (e.g., avoiding application before a rain) and maintaining soil pH above 6.5 may decrease N2O emissions. Biofiltration, separation of solids and liquid (followed by aerated composting), earthworm processing, and addition of nitrite-oxidizing bacteria are promising mitigation technologies for manure treatment.
Increasing animal production in developing countries can be a very successful strategy for mitigating GHG emissions from the livestock sector. Improving forage quality, including grain in the diet, achieving the genetic potential of the animal through proper nutrition, and use of local breeds or crossbreeds are recommended approaches for improving animal productivity and reducing GHG emissions per unit of product. The potential of using residual feed intake (RFI) as a selection tool for low CH4-emitters is an interesting mitigation option, but currently there is little evidence that low-RFI animals have a lower CH4 yield per unit of feed intake or product. Therefore, the immediate gain in GHG reductions through RFI is considered uncertain. Improved animal health and reduced mortality and morbidity are expected to result in increased animal production diluting non-CO2 emissions per unit product.
Lastly, interactions among individual components of livestock production systems are very complex, but must be considered when recommending GHG mitigation practices. One practice may successfully mitigate enteric CH4 emission, but increase fermentable substrate for increased GHG emissions from stored or land applied manure. Some mitigation practices are synergistic and are expected to decrease both enteric and manure GHG emissions (for example, improved animal health and animal production).