Co-author: Ishaya Gadzama
Summary
Enteric methane emissions from ruminant livestock significantly contribute to global greenhouse gas emissions. To mitigate these emissions, it's crucial to accurately quantify them. While mathematical models are commonly used for this purpose, selecting the most appropriate model is essential for obtaining accurate estimates. The INRA Tier 3 model offers a more accurate and flexible approach to quantifying enteric methane emissions from beef cattle compared to the IPCC Tier 2 model.
Introduction
Greenhouse gas (GHG) emissions, particularly methane (CH4), have become a focal point of global concern due to their impact on climate change (Sathaye et al., 2006). Livestock, especially ruminant animals such as cattle, are major contributors to these emissions, with enteric fermentation being the primary source (Broucek, 2014; Makombe & Gadzama, 2024). Enteric methane, produced during the digestion process in ruminants, has a global warming potential 25 times greater than carbon dioxide (CO2) (Lee et al., 2012), highlighting the urgency of mitigating these emissions.
Farmers and livestock producers should begin accurately quantifying enteric methane emissions, which is essential in order to develop effective mitigation strategies, improving the sustainability of livestock production, and meeting regulatory requirements (Madungwe, 2021). Several methods exist to measure methane emissions, but mathematical models have gained prominence due to their practicality and cost-effectiveness (Storm et al., 2012). However, the accuracy of these models relies heavily on the chosen methodology and the specific parameters considered.
This article explores two models for quantifying enteric methane emissions in beef cattle: the IPCC Tier 2 model and the INRA Tier 3 model (IPCC, 2006; Eugène et al., 2019). Both models have been described and compared in a research study conducted at Chinhoyi University of Technology (Madungwe, 2021).
The IPCC Tier 2 Model: A Widely Used Approach
The IPCC (Intergovernmental Panel on Climate Change) Tier 2 model is widely used for estimating enteric methane emissions. This model calculates emissions based on an animal's daily gross energy or dry matter intake and a predefined methane conversion rate (IPCC, 2006).
Advantages of IPCC Tier 2
The model is relatively simple to use and requires basic input data and it is internationally recognized and recommended by the IPCC.
Limitations of IPCC Tier 2
The IPCC Tier 2 model relies on default values for methane conversion rates, which may not accurately reflect the specific conditions of various production systems, diets, and animal breeds. Research suggests that the IPCC Tier 2 model may overestimate enteric methane emissions (Madungwe, 2021).
INRA Tier 3 Model: A More Refined Approach
The INRA (French Institute of Agriculture Research) Tier 3 model offers a more refined approach to quantifying enteric methane emissions. This model considers a wider range of factors, such as:
- Digestible Organic Matter Intake: It focuses on digestible organic matter intake rather than total dry matter intake, eliminating the error associated with undigested matter.
- Animal Factors: The model takes into consideration animal body weight and growth stage, as their influence on methane emissions is important.
- Production System: It considers the specific production system, acknowledging variations in diet composition and nutritional value.
Advantages of INRA Tier 3
- Accuracy: The INRA Tier 3 model usually provides more accurate estimates of enteric methane emissions as it considers a wider range of factors.
- Flexibility: The model's ability to accommodate variations in feeding levels and concentrate percentages makes it more adaptable to diverse production systems.
- Reduced Uncertainty: Calculating methane conversion factors based on specific conditions helps minimize the uncertainty that comes with relying on default values.
Limitations of INRA Tier 3
The model requires more detailed input data compared to the IPCC Tier 2 model, and it has not been widely adopted compared to the IPCC Tier 2 model.
Comparison of the Two Models
The research study by Madungwe (2021) compared the two models and found that the INRA Tier 3 model estimated significantly lower enteric methane emissions compared to the IPCC Tier 2 model. This finding supports the notion that the IPCC Tier 2 model may overestimate emissions, potentially due to its reliance on default values and its failure to account for digestible organic matter.
Implications for Farmers
Farmers should begin to accurately quantify the enteric methane emissions as it is important for various reasons. Some of them can be seen below:
- Develop Mitigation Strategies: Precise measurements enable farmers to identify and implement effective strategies to reduce methane emissions from their livestock.
- Improve Sustainability: Farmers can and should minimize methane emissions and can contribute to environmental sustainability and reduce their carbon footprint.
- Meet Regulatory Requirements: In regions with regulations on greenhouse gas emissions, accurate quantification is necessary for compliance.
Conclusion
The INRA Tier 3 model offers a more accurate and flexible approach to quantifying enteric methane emissions from beef cattle compared to the IPCC Tier 2 model. By considering factors such as digestible organic matter intake, animal characteristics, and production systems, it provides more precise estimates, enabling farmers to better understand and manage methane emissions from their livestock. While the INRA Tier 3 model may require more detailed input data, its enhanced accuracy and adaptability make it a valuable tool for improving the sustainability of beef cattle production.
References
- Broucek, J. (2014). Production of methane emissions from ruminant husbandry: a review. Journal of Environmental Protection, 5(15), 1482.
- Eugène, M., Sauvant, D., Noziere, P., Viallard, D., Oueslati, K., Lherm, M., ... & Doreau, M. (2019). A new Tier 3 method to calculate methane emission inventory for ruminants. Journal of Environmental Management, 231, 982-988.
- IPCC (2006). IPCC guidelines for national greenhouse gas inventories. Eggelston, S., Buendia, L., Miwa, K., Ngara, T., & Tanabe, K. (Eds.). Institute for Global Environmental Strategies (IGES) for the IPCC. https://www.ipcc.ch/report/2006-ipcc-guidelines-for-national-greenhouse-gas-inventories/
- Lee, J., Gereffi, G., & Beauvais, J. (2012). Global value chains and agrifood standards: Challenges and possibilities for smallholders in developing countries. Proceedings of the National Academy of Sciences, 109(31), 12326-12331.
- Madungwe, C. (2021). Comparing two indirect methods for quantifying entering methane emissions in beef cattle. Chinhoyi University of Technology.
- Makombe, W. S. & Gadzama, I. U. (2024). Brewer’s grain as a sustainable feed supplement: Reducing methane emissions in goats and cattle. Wikifarmer. Retrieved from https://www.researchgate.net/publication/386572675_Brewer’s_Grain_as_a_Sustainable_Feed_Supplement_Reducing_Methane_Emissions_in_Goats_and_Cattle
- Sathaye, J., Shukla, P., & Ravindranath, N. (2006). Climate change, sustainable development and India: Global and national concerns. Current Science, 90(3), 314–325.
- Storm, I. M., Hellwing, A. L. F., Nielsen, N. I., & Madsen, J. (2012). Methods for measuring and estimating methane emission from ruminants. Animals, 2(2), 160–183.