Methane emissions of cows under different livestock farming systems in Nagpur

Introduction

The livestock sector forms the backbone of rural livelihoods and significantly contributes to the agricultural economy in India. Ruminants are recognized as the primary contributors to methane emissions globally. India possesses the largest populations of buffalo and goats and ranks second in cattle and sheep populations worldwide (FAOSTAT, 2023) [7] . Methane is produced during the digestive process of ruminant animals such as cattle as a natural byproduct of enteric fermentation. As a potent greenhouse gas, methane (CH 4 ) plays a critical role in atmospheric processes and climate change. Its global warming potential is approximately 28 times higher than that of carbon dioxide (CO 2 ) (IPCC, 2022; MoEFCC, 2021) [13,18] . Due to its vast livestock population, India is a major contributor of methane emissions arising from enteric fermentation and manure handling. Additionally, methane contributes to global warming and acts as a precursor in the formation of tropospheric ozone (Francoeur et al., 2021; Manahan, 2017) [8,17] . In ruminant animals, nearly 95% of methane is released through the mouth and nostrils, with the remaining 5% emitted through the anal canal. Methane is formed during the anaerobic digestion of cellulose and other feed components by methanogenic bacteria, which use hydrogen (H 2 ) produced in the rumen. The amount of methane produced depends on the nature of fermentable carbohydrates and the balance between propionic and acetic acid production (Lassey, 2017; Jha et al., 2011) [16,14] . Methane formation results in a loss of energy that could otherwise support animal productivity. This process is known as "enteric fermentation." In addition, methane emissions also arise from manure management systems in livestock farming Various studies have estimated greenhouse gas emissions from India's livestock sector using different methodologies (Chhabra et al., 2009; Patra, 2012; Singhal et al., 2005; Swamy and Bhattacharya, 2006) [2,20,21,22] . Globally, livestock contributes 14.5% of GHG emissions, with 40% attributed to enteric methane from cattle (Tee et al., 2022) [23] . India's National GHG Inventory indicates that enteric fermentation produces around 130-140 million metric tons of CO 2 -equivalent methane annually. In 2020, emissions were estimated at 222,632 Gg CO 2 e, a slight decline of 0.28% compared to 2019 (Department of Animal Husbandry and Dairying, 2014; 2019) [4,5] . According to the IPCC (2022) [13] , India is one of the largest emitters of methane due to its substantial cattle and buffalo populations. Livestock contributes about 48% of national methane emissions, followed by the waste sector (20%) and rice cultivation (15%) (GHG Platform India, 2022) [10] . Enteric methane emissions are largely influenced by livestock population size, with higher animal numbers leading to increased emissions. Additional factors such as diet, topography, energy intake, and body weight also affect methane production. Hence the present study was undertaken to estimate the methane emissions of cows in different livestock farming systems in Nagpur.

Materials and Methods

Location of the study area:

The present study was conducted on the different livestock farming systems in different tehsils of Nagpur district, Maharashtra.

Collection of data:

The study utilized both traditional survey methods and direct field observations to collect data from the livestock farming systems. A comprehensive interview schedule was developed based on the study objectives to gather information on the general profile of the LFS including, size, daily milk yield, livestock population, and prevailing management practices.

Estimation of methane emission using IPCC methodology:

As per the Intergovernmental Panel for Climate Change (IPCC, 2006) [11] guidelines, methane emissions from cattle arising from enteric fermentation can be estimated using two standardized approaches, known as the Tier-1 and Tier-2 methodology.

Tier-1 method: The Tier-1 method is considered the simplest and most widely adopted approach for estimating methane emissions. It uses default emission factors developed by the IPCC (2006) [11] for different livestock categories. In IPCC Tier-1 methodology, country-wise livestock category-wise specific emission factors are available.

Enteric fermentation emissions from a livestock category

E T = methane emissions from Enteric Fermentation in animal category T, Gg CH 4 yr -1 EF (T, P) = emission factor for the defined livestock population T and the productivity system P, in kg CH 4 head - 1 yr -1 N (T, P) = the number of head of livestock species/category T in the country classified as productivity system P T = species/category of livestock P = productivity system, either high or low productivity for use in advanced Tier-1.

Emission of methane based on Tier-1 system:

There are three steps for the calculation of Tier-1 system: Step-1: Categorization and estimation of cattle population. Step-2: Emission factor collection from IPCC guidelines. IPCC-2019 provide emission factors for both average emission factor. Then we comparedthe calculation obtained from considering both emission factor. Step-3: Estimation of total methane emission by multiplying cattle population with emission factors.

Tier-2 Method

The Tier-2 approach is an enhanced approach that necessitates knowledge of animal categories, production and feeding methods, and manure management. Feed intake data for a representative animal in each class are needed for Tier-2 method. Typically, feed intake is expressed as dry matter (e.g., kilograms (kg) or gross energy (e.g., mega joules (MJ)) ingested daily. According to Eggelosten et al. (2019), the Tier-2 approach consists of three steps.

Steps 1: Data on the livestock population (including animal population and associated activity data) were obtained.

Steps 2: The methane conversion factor and dry matter intake for each animal group was used to estimate the emission factors. According to the Tier-2 approach, the emission factor must be determined by completing the subsequent sub-steps.

Step 3: To estimate total emissions, the selected emission factors was multiplied by the associated animal population and summed. As described above under Tier-1, the emissions estimates were reported in gigagrams (Gg). Step-2 (Emission factor development): For the development of emission factor, DMI value is required. Again, to estimate DMI the data of body weight followed by estimated dietary net energy concentration of the feed or diet (NE mf ) is needed.

Calculation of methane emission based on dry matter intake: Emission Factor (EF) = DMI ˟(

Step-3 (Total emission calculation): Total emission was calculated by multiplying the number of cattle with emission factor.

Results

Methane emissions by cows at different livestock farming system using IPCC Tier-1 method

The mean methane emissions estimated by Tier-1 method for lactating cows were recorded as 461.077±20. [3] , who documented enteric methane emissions of 232 kg CH 4 yr -1 in smallholder LFS, 812 kg CH 4 yr -1 in medium LFS, and 8120 kg CH 4 yr -1 in large LFS. The differences might be attributed to average herd size.

Methane emissions by animals at different livestock farming system using IPCC Tier-2 (Gross Energy) method Using Tier-2 (Gross Energy), the mean methane emissions of lactating cows were 850.004±37.529 kg CH 2023) [1] , who reported the enteric methane emissions of 856 kg CH . The results from Aydin and Koknaroglu (2023) [1] were used to compare outcomes for methane emissions from both Tier-2 (Gross Energy) and Tier-2 (Dry Matter Intake) method. The mean bearing different superscripts (a,b,&c) within the columns differs significantly (p<0.01)

Conclusion

The study concludes that methane emissions from enteric fermentation in the Nagpur district are strongly dependent on farm size, with larger livestock farming systems contributing disproportionately higher emissions. The significant differences (p<0.01) observed across farm categories highlight the need for differentiated mitigation strategies. Emission estimates obtained through Tier-2 approaches, especially Tier-2(Dry Matter Intake), were notably higher than Tier-1 estimates, emphasizing the importance of detailed and region-specific data for accurate quantification. Lactating cows were identified as the major emission contributors, suggesting the need for focused interventions in this group. From a policy perspective, promoting climate-smart livestock practicessuch as improved feed efficiency, inclusion of methane inhibitors, and balanced breeding strategies involving indigenous and crossbred cows is crucial in reducing methane emissions while sustaining productivity.

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