Measuring Carbon Emissions from Green and Low-Carbon Full-Life-Cycle Feeding in Large-Scale Pig Production Systems: A Case Study from Shaanxi Province, China

Abstract

In the pursuit of establishing a more environmentally sustainable and low-carbon hog farming system, the accurate quantification of emissions of greenhouse gas emanating from these systems, especially within the context of China, becomes imperative. Here, drawing insights from a life cycle approach, exhaustive field surveys, and context-specific analyses, we establish an emission measurement index system tailored to hog farming enterprises in China’s Shaanxi Province. Using this methodology, we probed the emission profiles and characteristics of three emblematic hog farming enterprises in the region. Our key findings are as follows: (1) The carbon dioxide emissions per kilogram of pork, factoring in feed cultivation, processing, and transportation, for Pucheng Xinliu Science and Technology, Baoji Zhengneng Farming, and Baoji Zhenghui Farming were quantified as 0.80298 kg, 1.52438 kg, and 0.81366 kg, respectively. (2) Presently, the methane emission coefficient due to enteric fermentation in large-scale hog farms in Shaanxi surpasses the default value set by the Intergovernmental Panel on Climate Change (IPCC). There appears to be a consistent underestimation of enteric methane emissions from live pigs in the province, as gauged against the IPCC metrics. Notably, the emission factor for fattening pigs averaged 2.61823 kgCH₄/head/year, while that for breeding pigs stood at 2.96752 kgCH₄/head/year. (3) When examining methane and nitrous oxide outputs from manure across various production stages, we observed that emissions from lactating pigs significantly outweigh those from other stages. Interestingly, nitrous oxide emissions from breeding pigs during fattening, finishing, and gestation remained nearly the same, regardless of the manure treatment method. (4) Under the management protocols followed by Pucheng and Baoji, the total carbon emissions from an individual fattening pig amounted to 328.5283 kg and 539.2060 kg, respectively, whereas for breeding pigs, these values were 539.2060 kg and 551.6733 kg, respectively. Further calculations showed that the average carbon footprint CF of large-scale pig farms in China was 3.6281 kgCO₂/kg pork. In conclusion, optimizing feed cultivation and transportation logistics, promoting integrated breeding and rearing practices, refining feed formulation, and advancing manure management practices can collaboratively attenuate greenhouse gas emissions. Such synergistic approaches hold promise for steering the hog industry towards a greener, low-carbon, and sustainable trajectory.

1. Introduction

The international community is grappling with the escalating challenges posed by climate change, largely driven by emissions of greenhouse gases such as CO₂, CH₄, and N₂O. The repercussions of these changes encompass ecological and environmental degradation, threats to human health and wellbeing, and hindrances to socio-economic progression [1]. In response to these impending challenges, China has charted the ambitious “dual-carbon” objective, aiming for a peak in carbon emissions by 2030 and neutrality by 2060 [2,3]. While significant emphasis is placed on the carbon footprints of the secondary and tertiary economic sectors, the agricultural sector, often overlooked, plays a non-trivial role. The United Nations Framework Convention on Climate Change (UNFCCC) underscores that agriculture contributes to 13% of global carbon emissions, as documented in its 2019 report “Climate Action and Support Trends” [4,5]. An aspect of agriculture demanding critical attention is livestock and poultry farming, which is integral for ensuring food security and fostering agricultural growth. Remarkably, this segment alone is estimated to be responsible for 54.3% of total agricultural carbon emissions [6,7]. Thus, a holistic approach to global greenhouse gas mitigation necessitates earnest engagement with the livestock and poultry sectors. Achieving a sustainable, green trajectory for the livestock and poultry industry involves rigorous carbon accounting across its multifaceted production chain [8,9,10]. This requires meticulous analyses of greenhouse gas emission intensities and the carbon footprint of diverse livestock and poultry varieties across varied production scales.

China’s hog farming industry stands at the forefront of its livestock and poultry sector, both in terms of production magnitude and as a significant contributor to greenhouse gas (GHG) emissions [11,12,13]. Innovations and shifts in farming practices have propelled the hog industry towards enhanced scales of specialization, intensification, and efficiency. This evolution, which encompasses improved feed conversion rates and truncated hog growth cycles, complicates the precise quantification of the industry’s GHG outputs [14,15]. Following the IPCC’s GHG quantification framework, with fixed slaughter capacity and emission factors, the GHG emissions from hog farming predominantly hinge on the duration of the pig rearing cycle. Beyond direct emissions from pig production, other integral facets, such as on-farm energy utilization and the entire feed production-to-transportation continuum, are consequential GHG contributors. Consequently, a methodologically robust approach to GHG measurement mandates a comprehensive understanding of the entire pig farming system, encapsulating all pivotal production components [16,17].

The academic realm offers an abundance of research dedicated to quantifying greenhouse gas (GHG) emissions from livestock and poultry farming. Recent methodologies have evolved by integrating multiple approaches, including the OECD’s measurement framework, the IPCC’s national GHG inventory method, and the life cycle assessment (LCA) technique, all aiming to enhance the precision of GHG evaluations in the livestock sector [18,19,20]. Prominently, the LCA methodology, acknowledged globally, provides an encompassing lens for assessing GHG emissions across a product’s lifespan. It has been adeptly applied to model GHG dynamics within various livestock sectors, accommodating regional nuances and diverse production scales [17,21,22]. This technique holistically spans the entirety of livestock production, from raw material acquisition, progressing through varied production stages, and culminating at the product’s end use [23,24]. The expansion of China’s hog farming industry has inevitably placed its GHG contributions under academic scrutiny [25,26]. Implementing the LCA approach for GHG quantification in this sector necessitates delineating the emission accounting boundary and subsequent calculation of GHG emissions [27,28]. Considering the diversity of hog breeds and feeding structures across Chinese enterprises, a clear definition of farming species and practices becomes indispensable. Post this delineation, the task is to pinpoint GHG sources and types, allowing the selection of suitable accounting methods, followed by data aggregation and emission calculations [29]. While the cited studies provide foundational insights, there remains a conspicuous gap in the literature centered on large-scale, intensive pig farming GHG measurements. The academic sphere is still grappling with challenges such as inconsistent accounting standards, vague methodologies, and an absence of a defined accounting process. Urgently addressing these lacunae, while tailoring a GHG measurement system that resonates with China’s unique pig farming landscape and discerning emission factors across various stages, is paramount for future research endeavors [30].

During its phase of expansive growth, understanding and quantifying the greenhouse gas (GHG) emissions across all facets of China’s hog farming industry have become pivotal. Such insights, especially the specific GHG contributions of individual sectors within the production chain, are instrumental in steering the industry towards eco-friendly and carbon-minimal practices, particularly within the realm of large-scale farming enterprises. To this end, our study focuses on major farming enterprises within Shaanxi Province, China. By integrating the nuances of pig farming with regional specificities, we establish a carbon emission measurement index, rooted in the life cycle evaluation technique. This framework, influenced by the IPCC 2006 Guidelines for National Greenhouse Gas Inventories and contemporary research, aims to scrutinize the GHG emissions and their unique characteristics within the pig farming landscape. Utilizing 2021 production data from three representative pig farms in Shaanxi Province, this study delves into the GHG dynamics of the province’s pig farming system. Furthermore, we explore the current trajectories of carbon emissions alongside potential optimization pathways. Our overarching goal continues to be to bolster theoretical underpinnings that champion a sustainable, low-carbon future for the pig farming sector in order to realizing carbon mitigation through a harmonized approach that melds supply stability with green innovation.

In this study, we present a nuanced approach to measuring carbon emissions in large-scale pig breeding enterprises. By integrating the life cycle method with the economic coefficient method and direct measurement techniques, our work significantly refines the existing measurement formulas. We delineate the boundaries of carbon emissions specific to this sector, providing a detailed breakdown of the different phases in pig breeding, including the nursery and fattening periods for fattening pigs, and the nursery, fattening, reserve, gestation, and lactation periods for breeding pigs. Crucially, our methodology tailors carbon emission measurement formulas to the distinct feeding strategies employed across various production phases. Taking varying feed ratios during the production period into account allows for a more precise and comprehensive estimation of carbon emissions. Our findings offer empirical evidence for the refined calculation of carbon emissions in large-scale pig farming, particularly pertinent to developing countries. This advancement in measurement techniques represents a significant contribution to environmental impact assessments within the agricultural sector, providing a more accurate tool for evaluating and mitigating carbon footprints in large-scale farming operations.

2. Materials and Methods

2.1. Data Source

The core data underpinning this research were sourced from the IPCC guidelines, complemented by datasets from the research initiative titled “Research, Development and Integrated Demonstration of Green and Low-Carbon Breeding Technologies for Typical Livestock and Poultry Breeds”. Addressing the challenge of unidentified carbon sources and sinks, coupled with pronounced environmental pollution due to the disconnect between cultivation and farming, the research team delved into the dynamics of integrated low-carbon development across typical livestock and poultry breeds. The outcome was an innovative, green, and low-carbon cyclical model spanning feed cultivation, livestock and poultry breeding, and arable land cultivation. This model, geared towards balancing waste, was tailored for varied scales of livestock and poultry breeds prevalent in Shaanxi Province.

For empirical evaluation of this integrated recycling model, three emblematic hog farming enterprises within Shaanxi Province were chosen: Pucheng Xinliu Technology Co., Ltd., Weinan, China, Baoji Zhengneng Agricultural and Animal Husbandry Technology Co., Ltd., Baoji, China, and Baoji Zhenghui Agricultural and Animal Husbandry Technology Co., Ltd., Baoji, China. In this study, the selection of the three pig farms for analysis was performed with a focus on typicality and representativeness within the context of modern Chinese agriculture. Each farm is a regional subsidiary of the Beijing Dabeinong Group in Shaanxi Province, a nationally recognized leader in agricultural industrialization in China. These farms exemplify the cutting-edge integration of hog farming with the development and production of feed, as well as sales operations, characterizing them as modern large-scale farming enterprises. This choice underpins this study’s relevance to current agricultural practices and provides a solid foundation for extrapolating findings to a broader industrial context.

Comprehensive engagement with these entities involved interviews with executive leadership, frontline technical personnel, and other pertinent stakeholders. The objective was to glean insights into the enterprise’s farming methodologies, breeding scale, and operational paradigms. On-site evaluations of production lines were imperative, ensuring the precise quantification of greenhouse gas emissions throughout the value chain, encapsulating feed production, pig respiratory and fermentation processes, manure management, and overall energy expenditures on the farms.

2.2. Boundary Determination

In assessing greenhouse gas (GHG) emissions from pig farming, it is crucial to encapsulate not just the direct carbon emissions—notably CH₄ from enteric fermentation and CH₄ and N₂O emissions from manure management—but also the indirect carbon emissions stemming from intertwined production systems like energy consumption and feed production. An in-depth emission analysis thus warrants a holistic view of the pig farming system, incorporating every production phase. Central to the life cycle approach is the precise establishment of research goals and judicious demarcation of system boundaries. The scope of these boundaries in hog farming profoundly influences the outcomes and implications of the ensuing evaluation [31]. Guided by the study’s objectives, this research emphasized CO₂, CH₄, and N₂O, three GHGs intimately linked to pig farming. Building on the existing literature [29,32], the system boundary for pig farming was delineated from the inception of feed production to the “farm gate” of pig dispatch. This encompassed two primary modules and three interconnected stages: (1) The Feed Production Module: This captured direct or indirect CO₂ emissions originating from input elements like pesticides, fertilizers, and fuels during feed crop cultivation. Additionally, CO₂ emissions from energy usage in the processing and transportation of feed were integrated. (2) The Pig Production Module: This section accounted for CH₄ emissions from pigs’ enteric fermentation, CH₄ and N₂O emissions from various manure treatment techniques, and CO₂ emissions indirectly resulting from energy consumption at farms. The schematic representation of the boundaries established for the hog farming system in this study is visualized in Figure 1.

2.3. Greenhouse Gas Formula for Pig Farming

Informed by the preceding evaluations, this study seamlessly integrated the IPCC measurement approach with the life cycle methodology. Drawing on pertinent research, and aligning with farm-specific contexts and the availability of index data, we categorized the primary entities of pig breeding into two distinct classifications: fattening pigs and breeding pigs. Among them, the growth cycle of fattening pigs was T (day), the weight was W₁ (kg), and the time of the nursery and fattening period in the rearing stage was T₁ (day) and T₂ (day), respectively. The growth cycle of breeding pigs was T (day), the weight was W₂ (kg), and the time of the nursery, fattening, reserve, gestation, and lactation period in the rearing stage was T₁ (day), T₂ (day), T₃ (day), T₄ (day), and T₅ (day), respectively.

2.3.1. Greenhouse Gas Emissions from Feed Production, Processing and Transportation

Given the specific circumstances of the farms under investigation, the feed production aspect of this research was constrained to GHG emissions arising from the cultivation and processing of three principal feed components: corn, soybean meal, and wheat bran. The documented annual consumption of component feed (i) by the farm wa Y_i kg. This translates to a consumption rate of ‘1’ per kilogram of pork, denoted as ‘Feed’.

$$\sum {\mathrm{F}\mathrm{e}\mathrm{e}\mathrm{d}}_{\mathrm{i}}=\frac{{\mathrm{Y}}_{\mathrm{i}}}{{\mathrm{N}}_1\times {\mathrm{W}}_1+{\mathrm{N}}_2\times {\mathrm{W}}_2}$$

(1)

where N₁ is the number of fattening pigs farrowed on the farm in one year; W₁ is the average weight of fattened pigs farrowed; N₂ is the number of breeding pigs farrowed on the farm in one year, and W₂ is the average weight of breeding pigs farrowed.

Greenhouse gas (GHG) emissions originating from agricultural inputs during feed crop cultivation encompass CO₂ emissions associated with the manufacture of agricultural films, pesticides, and fertilizers. Additionally, CO₂ emissions resulting from the energy utilization of agricultural machinery and irrigation systems are integral to this assessment.

• Greenhouse gases from fodder crop cultivation

$${\mathrm{C}\mathrm{O}}_2=\mathsf{\Sigma }\frac{{\mathrm{F}\mathrm{e}\mathrm{e}\mathrm{d}}_{\mathrm{i}}}{{\mathrm{R}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}}_{\mathrm{i}}\times {\mathrm{Y}\mathrm{P}\mathrm{U}}_{\mathrm{i}}}\times {\mathrm{Z}}_{\mathrm{i}}\times {\mathsf{\beta }}_{\mathrm{i}}\times \mathrm{E}\mathrm{F}$$

(2)

In Equation (2), Feed_i is the consumption of feed (i) per kilogram of pork (kgFeed/kg); Ratio_i is the proportion of feed crops (i) processed into raw materials; YPU_i is the average yield per acre of feed crops (i) (kg/mu); Af_i is the consumption of agro-films, pesticides, nitrogen-phosphorus-potassium (NPK) fertilizers, compound fertilizers, and diesel oil of feed crops (i) (kg/mu); β_i is the economic allocation coefficient of feed crops (i); and EF is the GHG emission factor of agro-films, pesticides, NPK fertilizers, compound fertilizers, and diesel oil (kgCO₂/kg).

2.

Greenhouse gas emissions from feed transportation

Emissions from the consumption of diesel fuel during the transportation of feed to the piggery were calculated using the following formula:

$${\mathrm{E}}_{\mathrm{c}}=\mathrm{T}\mathrm{D}\times \mathrm{A}\mathrm{D}\times {\mathrm{E}\mathrm{F}}_{\mathrm{E}\mathrm{l}}$$

(3)

In Equation (3), E_C is the annual CO₂ emission from transportation kg/a; TD is the annual transportation distance km/a; AD is the consumption of diesel fuel per kilometer kg; and EF_EI is the CO₂ emission coefficient of diesel fuel combustion in the transportation process.

2.3.2. Methane Emissions from Enteric Fermentation

In the literature, there exists a notable paucity of studies addressing the enteric fermentation emission factor, total energy, and enteric methane conversion rate for swine. A substantial portion of the prevailing research relies on IPCC guidelines, which standardize the swine production cycle at 365 days. Such a generalization may be overly simplistic, given the variations attributed to swine breeds and distinct farm feeding practices. In response to this limitation, our investigation integrated the IPCC framework with insights from prior research [17,33]. This integrative approach allowed us to refine and segment the swine feeding cycle, aiming to achieve enhanced precision in our estimates. We employed the subsequent equations for our estimations:

$${\mathrm{C}\mathrm{H}}_4=\mathsf{\Sigma }({\mathrm{E}\mathrm{F}}_{\mathrm{i}}\times {\mathrm{T}}_{\mathrm{i}})/\mathrm{W}$$

(4)

In Equation (4), CH₄ is the methane emission from enteric fermentation per kilogram of pig (kgCH₄/kg); EF_i is the methane emission factor from enteric fermentation of pigs at different stages (i) (kgCH₄/head/day); T_i is the methane emission factor from enteric fermentation at different growth cycle (day) at different stages (i); and W is the weight of hogs (kg/head). The specific calculation process for EF_i is described in Equations (S1) and (S2) in the Supplementary Materials.

2.3.3. CO₂ Emissions from Farm Energy Consumption

Within the porcine agricultural process, the predominant energy sources encompass electricity and fossil fuels. Current empirical evidence, coupled with investigations specific to Shaanxi Province, elucidates that pig farms predominantly outsource their electricity needs. The fossil fuels in utilization principally comprise gasoline, diesel, and coal. CO₂ emissions derived from the combustion of these fossil fuels are categorized as direct emissions, while those stemming from electrical consumption are deemed indirect emissions. Consequently, the CO₂ emissions associated with farm energy consumption were bifurcated into direct and indirect categories for subsequent calculations:

$${\mathrm{E}}_{\mathrm{E}\mathrm{I}}=\mathrm{E}\mathrm{D}\times {\mathrm{E}\mathrm{F}}_{\mathrm{E}\mathrm{l}}$$

(5)

Equation (5) is the indirect emission calculation formula, where E_EI represents the total CO₂ emissions due to net purchased electricity in pig farm production (tCO₂); ED is the net purchased electricity in production (MWh); and EF_EI is the electric CO₂ emission factor (tCO₂/MWh), because Shaanxi Province belongs to the Northwest region of China, the 2019 purchased electricity emission factor of the Northwest China Regional Power Grid is taken to be 0.8922 kgCO₂/KWh.

$${\mathrm{E}}_{\mathrm{B}}=\mathsf{\Sigma }{\mathrm{F}\mathrm{C}}_{\mathrm{F},\mathrm{i}}\times {\mathrm{N}\mathrm{C}\mathrm{V}}_{\mathrm{F},\mathrm{i}}\times {\mathrm{C}\mathrm{C}}_{\mathrm{I}}\times {\mathrm{O}\mathrm{F}}_{\mathrm{i}}\times \frac{44}{12}$$

(6)

Equation (6) is the direct emission calculation formula, where E_B represents the total CO₂ emissions due to fuel combustion in swine farm management (kgCO₂/head of fattening pig), i is the ith fossil fuel, FC_F,i is the amount of fossil fuel i consumed per pig raised on the farm (kg/head of fattening pig), NCV_F,i is the low-lying calorific value of the ith fossil fuel (GJ/t), OF_i is the carbon content of the unit calorific value of the ith fuel (tC/GJ), and 44/12 is the ratio of molecular weights of CO₂ to C.

2.3.4. Greenhouse Gas Emissions from Manure Management

• Greenhouse gases from fodder crop cultivation

$${\mathrm{C}\mathrm{H}}_{4\left(\mathrm{mm}\right)}=\frac{\mathsf{\Sigma }\left({\mathrm{E}\mathrm{F}}_{\mathrm{i},{\mathrm{C}\mathrm{H}}_4}\right)}{\mathrm{W}}$$

(7)

CH_{4 (mm)} represents the methane emissions per kilogram of feces produced by pigs (kgCH₄/kg); ${\mathrm{E}\mathrm{F}}_{\mathrm{i},{\mathrm{C}\mathrm{H}}_4}$ is the methane emission factor of feces produced by pigs at different stages (i) (kgCH₄/head/day); and W is the weight of pigs (kg/head).

$${\mathrm{E}\mathrm{F}}_{\mathrm{i},\mathrm{j}}={\mathrm{V}\mathrm{S}}_{\mathrm{i}}\times {\mathrm{B}}_{{\mathrm{C}\mathrm{H}}_4}\times \frac{0.67\mathrm{k}\mathrm{g}}{{\mathrm{m}}^3}\times {\mathrm{T}}_{\mathrm{i}}\times {\mathrm{M}\mathrm{C}\mathrm{F}}_{\mathrm{i},\mathrm{j}}\times {\mathrm{M}\mathrm{S}}_{\mathrm{i},\mathrm{j}}$$

(8)

In Equation (8), EF_i,j is the methane emission factor produced by hogs in stage i under manure management method j, and VS_i is the daily volatile solid excretion (kg dry matter/head/day) of hogs producing manure at different stages (i); ${\mathrm{B}}_{{\mathrm{C}\mathrm{H}}_4}$ is the methane production capacity (m³CH₄/kgVS) in the manure of hog type i; 0.67 is the conversion factor of m³CH₄ to kgCH₄; MCF_i,j is the methane conversion factor (%) of the jth type of manure management; MS_i,j is the proportion of hogs of the i-th type that use the j-th type of manure management (%); and T_i represents different stages of the growth cycle (days). The specific calculations of ${\mathrm{V}\mathrm{S}}_{\mathrm{i}}$ and ${\mathrm{B}}_{{\mathrm{C}\mathrm{H}}_4}$ are shown in Equations (S3) and (S4) in the Supplementary Materials.

2.

Nitrous oxide emissions from manure management

$${\mathrm{N}}_2\mathrm{O}=\frac{\mathsf{\Sigma }\left({\mathrm{E}\mathrm{F}}_{\mathrm{i},{\mathrm{N}}_2\mathrm{O}}\times {\mathrm{T}}_{\mathrm{i}}\right)}{\mathrm{W}}$$

(9)

In Equation (9), N₂O represents the nitrous oxide emissions per kilogram of feces produced by pigs (kgN₂O/kg); $\mathrm{E}{\mathrm{F}}_{\mathrm{i} ,{\mathrm{N}}_2\mathrm{O}}$ is the methane emission factor of feces produced by pigs at different stages (i) (kgN₂O/head/day); Ti represents the growth cycle at different stages (i) (day); and W is the body weight of pigs (kg/head).

$${\mathrm{E}\mathrm{F}}_{\mathrm{i},{\mathrm{N}}_2\mathrm{O}}={\mathrm{V}\mathrm{S}}_{\mathrm{i}}\times {\mathrm{B}}_{{\mathrm{N}}_2\mathrm{O}}\times {\mathrm{M}\mathrm{S}}_{\mathrm{i},\mathrm{j}}\left(14\right)$$

(10)

In Equation (10), VS_i is the daily volatile solid excretion (kg dry matter/head/day) of manure produced by hogs at different stages (i), the specific calculation process for VS_i is shown in Equation (S3) in the Supplementary Materials; ${\mathrm{B}}_{{\mathrm{N}}_2\mathrm{O}}$ is the nitrous oxide production capacity of hogs per kilogram of manure produced (kgN₂O/kgVS); and MS_i,j is the proportion of hogs of species i that use type j of manure management practices (%).

3. Results and Analysis

3.1. Overview of the Basic Conditions of the Farm

This investigation spotlighted three representative pig farming enterprises in Shaanxi Province. Given the variances in production phases and feed provisions among fattening and breeding swine, these animals were categorically segmented into ‘fattening pigs’ and ‘breeding pigs’. Comprehensive statistics delineating the feeding magnitude and foundational data for each enterprise are articulated in

Table 1. Basic situation of pig rearing for fattening pigs on each farm.

Pig Fattening	Breed	Average Annual Stock/Head	Average Annual Output/Head	Average Weight at Barn/kg
Pucheng New Six Technology	PIC	24,000	300,000	120
Baoji Zhengneng Farming	none	none	none	none
Baoji Zhenghui Farming	Binary Pig	11,500	24,000	110

and

Table 2. Basic situation of pig breeding on each farm.

Pig Breeding	Breed	Average Annual Stock/Head	Average Annual Output/Head	Average Weight at Barn/kg
Pucheng New Six Technology	PIC	24,000	300,000	120
Baoji Zhengneng Farming	Binary Pig	5360	none	none
Baoji Zhenghui Farming	none	none	none	none

.

A perusal of Table 1 and Table 2 underscores the considerable production capacities of the triad, emblematic of regional operations. Specifically, Pucheng Xinliu Science and Technology’s on-site operations encompass dual production avenues, catering to both breeding and fattening pigs. Baoji Zhengneng specializes in breeding swine, whereas Baoji Zhenghui predominantly focuses on fattening procedures. Each enterprise maintains a singular feeding trajectory, predominantly housing breeds such as PIC and binary pigs.

In adherence to the earlier-introduced GHG estimation paradigm for swine cultivation, it is imperative to collate data reflecting the feeding duration, daily feed intake averages, and body weight metrics across diverse growth periods for both fattening and breeding pigs within these entities. These data, crucial for the formulaic computations, are cataloged in

Table 3. Basic information on fattening pig rearing in stages on each farm.

Pig Fattening	Total Feeding Period	Conservation Period Days and Average Daily Feed Intake kg/Head	Number of Days of Fattening Period and Average Daily Feed Intake kg/Head
Pucheng New Six Technology	180 day	30 day, 0.9 kg	150 day, 2.5 kg
Baoji Zhengneng Farming	none	none	none
Baoji Zhenghui Farming	140 day	30 day, 0.5 kg	110 day, 2.5 kg

and

Table 4. Basic information on the phased feeding of breeding pigs on each farm.

Pig Breeding	Total Feeding Period	Days of Conservation and Average Daily Feed Intake kg/Head	Fattening Days and Average Daily Feed Intake kg/Head	Days to Reserve and Average Daily Feed Intake kg/Head	Gestation Days and Average Daily Feed Intake kg/Head	Lactation Days and Average Daily Feed Intake kg/Head
Pucheng New Six Technology	348 day	56 day, 0.9 kg	104 day, 2.5 kg	50 day, 2.5 kg	114 day, 2.5 kg	24 day, 6.0 kg
Baoji Zhengneng Farming	385 day	25 day, 1.3 kg	130 day, 2.0 kg	92 day, 2.0 kg	114 day, 2.42 kg	24 day, 6.01 kg
Baoji Zhenghui Farming	none	none	none	none	none	none

, illustrating specifics for each pig type per farm.

An analysis of Table 3 and Table 4 elucidates that, on average, fattening pigs undergo a rearing process of approximately 160 days. While there are inherent breed-specific variations, the demarcation between the nursery and fattening growth phases remains largely consistent across the entities, with only marginal variances in feed allocations during these phases. Breeding pigs, conversely, exhibit a mean feeding span of one annum. While growth phase durations exhibit slight breed-induced fluctuations, the feed dispensation remains relatively uniform across these stages.

3.2. Calculation of Greenhouse Gas Emissions from Feed Production and Transportation

3.2.1. Greenhouse Gas Calculations for Feed Production Processes

In light of extant research, it has been discerned that emissions attributable to ancillary feed components are substantially diminished in comparison to emissions from predominant feedstuffs like corn, soybean meal, and wheat bran, which constitute a major fraction of swine feed. Consequently, this research predominantly quantifies the greenhouse gas (GHG) emissions concomitant with the cultivation and production of these three salient feed ingredients. Consolidating feed proportions from various mills facilitated the derivation of ingredient ratios for corn, soybean meal, and wheat bran, the outcomes of which are delineated in Figure 2.

GHG emissions affiliated with agricultural inputs during the cultivation of these feed crops encapsulate CO₂ emissions emanating from the production of agricultural films, pesticides, and fertilizers, complemented by CO₂ emissions derived from the energy outlay associated with agricultural machinery and irrigation. In the agricultural continuum, CO₂ emissions from these inputs should be equitably apportioned between primary and subsidiary products. The data indicate that the valuations for corn, soybeans, and wheat stand at CNY 2.31/kg, CNY 4.86/kg, and CNY 2.28/kg, respectively. An economic snapshot from December 2021 elucidated that corn, soybeans, and wheat are priced approximately at CNY 2500/ton, CNY 5000/ton, and CNY 2000/ton, respectively, while their by-products command different price points. Invoking economic value allocation principles [17], the allocation coefficients for corn, soybean meal, and wheat bran—pivotal in hog nutrition—are discerned to be 25/27, 26/76, and 8/28, respectively.

Agricultural inputs and their corresponding emission factors in the context of feed crop production have been extracted predominantly from extant Chinese datasets. Initial endeavors encompassed the statistical evaluation of the yields and agricultural inputs for corn, soybeans, and wheat specific to Shaanxi Province, as tabulated in

Table 5. Corn, soybean and wheat yields and fertilizer and other farm inputs in Shaanxi Province in 2020.

Measurement Indicators		Corn	Soybeans	Wheat
Yield per unit (kg/mu 1)		502.62	133.56	430.33
Proportion of crops processed for feedstock (ratio (%))		55	82	28
Fertilizer application rate (kg/mu)		24.97	8.46	28.33
Amount of agricultural film applied (kg/mu)		0.37	0	0
Discounted fertilizer use per mµ (kg/mu)	Nitrogen fertilizer (kg/mu)	6.46	1.02	7.73
	Phosphate fertilizer (kg/mu)	0.20	0.10	0.24
	Potash fertilizer (kg/mu)	0.14	0.48	0.02
	Compound fertilizer (kg/mu)	18.18	6.85	20.33
Pesticide application rate (kg/mu)	Pesticide fee (CNY/mu)	19.54	18.61	28.31
	Average pesticide prices (CNY/kg)	86.31
	Pesticide application rate per acre (kg/mu)	0.23	0.22	0.33
Diesel inputs (kg/mu)	Fuel and power costs (CNY/mu)	0.58	0.25	1.01
	Price of diesel oil (CNY/kg)	5.544
	Diesel fuel consumption per mu (kg/mu)	0.10	0.05	0.18
Electricity consumption for drainage and irrigation (kwh/mu)	Irrigation and drainage fees (CNY/mu)	16.79	1.11	33.24
	Water bill (CNY/mu)	6.14	0.09	5.28
	Electricity prices for irrigation and drainage (CNY/kwh)	0.2974
	Electricity consumption for drainage and irrigation (kwh/mu)	35.81	3.43	94.01

¹ mu = 1/15 ha.

. Subsequent to this, leveraging the pertinent literature [33,34], GHG emission factors corresponding to diverse facets of crop production were ascertained, and these findings are cataloged in

Table 6. GHG emission factors for different project types.

Project	Value	Unit
Nitrogen fertilizer	2.12	kgCO2/kg
Phosphate fertilizer	0.64	kgCO2/kg
Potash fertilizer	0.18	kgCO2/kg
Compound fertilizer	0.07	kgCO2/kg
Agro-film	22.72	kgCO2/kg
Agrochemicals	12.44	kgCO2/kg
Coals	1.98	kgCO2/kg
Diesel fuel	3.16	kgCO2/kg
Grids	0.67	kgCO2/kWh

.

Incorporating the aforementioned formula with the data from Figure 2 and Table 5 and Table 6, we derived the greenhouse gas emissions associated with the feed production processes across the studied farms. The outcomes, specifying the carbon dioxide emissions from the feed production endeavors of the three enterprises, are detailed in

Table 7. Pucheng Xinliu Technology feed production process CO₂ emissions.

Pucheng New Six Technology (kgCO2/kg)	Corn	Soybeans	Wheat	Total
Agro-film	0.05462	0	0	0.05462
Agrochemical	0.01859	0.00711	0.01618	0.04188
Nitrogen fertilizer	0.08898	0.00562	0.06461	0.15921
Phosphate fertilizer	0.00083	0.00022	0.00060	0.00165
Potash fertilizer	0.00017	0.00023	0.00001	0.00041
Compound fertilizer	0.00827	0.00125	0.00562	0.01514
Diesel fuel	0.00205	0.00038	0.00224	0.00467
Grids	0.15589	0.00597	0.24833	0.41019
Total	0.3294	0.02078	0.33759	0.68777

,

Table 8. Baoji Zhengneng Agriculture and Animal Husbandry feed production process CO₂ emissions.

Baoji Zhengneng Farming (kgCO2/kg)	Corn	Soybeans	Wheat	Total
Agro-film	0.09464	0	0	0.09464
Agrochemical	0.03221	0.01232	0.02803	0.07256
Nitrogen fertilizer	0.15418	0.00973	0.11194	0.27585
Phosphate fertilizer	0.00143	0.00037	0.00104	0.00284
Potash fertilizer	0.00029	0.00039	0.00002	0.0007
Compound fertilizer	0.01432	0.00216	0.00973	0.02621
Diesel fuel	0.00355	0.00067	0.00388	0.00810
Grids	0.27011	0.01034	0.43029	0.71074
Total	0.57073	0.03598	0.58493	1.19164

and

Table 9. Baoji Zhenghui Agriculture and Animal Husbandry feed production process CO₂ emissions.

Baoji Zhenghui Farming (kgCO2/kg)	Corn	Soybeans	Wheat	Total
Agro-film	0.04824	0	0	0.04824
Agrochemical	0.01642	0.00628	0.01429	0.03699
Nitrogen fertilizer	0.07859	0.00496	0.05706	0.14061
Phosphate fertilizer	0.00073	0.00019	0.00053	0.00145
Potash fertilizer	0.00015	0.00020	0.00001	0.00036
Compound fertilizer	0.00730	0.00110	0.00496	0.01336
Diesel fuel	0.00181	0.00034	0.00198	0.00413
grids	0.13768	0.00527	0.21933	0.36228
Total	0.29092	0.01834	0.29816	0.60742

.

Utilizing an integrative analysis of carbon dioxide emissions from the feed production processes across the studied farms, we observed that the CO₂ output per kilogram of pork, stemming from the production and processing of corn and wheat, considerably exceeds that of soybeans. This is likely attributable to the dominant presence of corn and wheat in the feed compositions. When evaluating the components of feed production and cultivation, notable CO₂ emissions arise, predominantly from the electricity utilized in drainage and irrigation, as well as from nitrogen fertilizer applications. To achieve meaningful reductions in carbon emissions within agricultural production, efforts should be strategically concentrated on these two sectors. In the pursuit of sustainable agriculture, developing countries are encouraged to prioritize the promotion of green and low-carbon practices in feed production. This approach is instrumental in advancing the overall ecological development of pig farming. A critical aspect of this strategy involves controlling carbon emissions right from the initial stages of feed cultivation. By focusing on reducing the carbon footprint at this fundamental phase, a significant downstream impact can be exerted on the carbon emissions from the entire pig farming process. Implementing such environmentally conscious practices not only aligns with global efforts to mitigate climate change but also sets a precedent for sustainable agricultural practices in the livestock sector.

3.2.2. Greenhouse Gas Calculations for Feed Transportation Processes

In the assessment of CO₂ emissions from the feed transportation process, we no longer differentiate based on individual feed ingredients. Instead, we aggregate the greenhouse gas emissions associated with the entirety of the feed. In alignment with the empirical context of this research, a diesel truck with a carrying capacity of 30 tons was chosen as the transportation means. The diesel consumption rate per kilometer was approximated at 0.25 kg. It is crucial to note that the transportation distance accounts for both the outbound and return journeys, necessitating a multiplication of the initial distance by two. The results derived from these computations are presented in

Table 10. Calculation results of CO₂ emissions from feed transportation at each site.

CO2 Emissions from Feed Transportation	Feed Annual Feed Consumption (t)	Transportation Distance (km)	Annual CO2 Emissions (kg)	CO2 Emissions per kg of Pork (kg)
Pucheng New Six Technology	27,000	87.5	497,700	0.11521
Baoji Zhengneng Farming	6120	166	214,020	0.33274
Baoji Zhenghui Farming	6192	200	260,889	0.20624

.

Upon scrutinizing the formulaic derivations and their subsequent outcomes, it becomes evident that the annual CO₂ emissions from the feed transportation process hinge predominantly on the frequency of transportation and the associated distances. Notably, the feed consumption and transportation lengths for both Baoji Zhengneng Farming and Baoji Zhenghui Farming are nearly analogous, leading to a marginal disparity in their total CO₂ emissions from their transportation operations. In addressing the imperative of reducing carbon emissions in hog farming, large-scale farms are advised to adopt an integrated “planting and farming” production model. This strategy entails expanding the land dedicated to fodder cultivation in proximity to the farms, enabling on-site fodder production. Such a localized approach to fodder growth not only minimizes the transportation distances but also plays a crucial role in the overall reduction in carbon emissions associated with hog farming. By implementing this model, farms can significantly contribute to sustainable agricultural development.

3.3. Calculation of Methane Emissions from Enteric Fermentation of Pigs on Farms

Utilizing the above-stated computational framework, in tandem with our survey findings, we derived methane emission outcomes from enteric fermentation for fattening and breeding pigs across each facility. In our calculations, based on individual production profiles of the respective companies, the feed moisture content during the fattening phase was fixed at 12%. In contrast, during other growth intervals, this figure stood at 14%. The proportion of the feed’s total energy that undergoes conversion into methane is determined at 0.8% for the fattening phase, whereas for other growth phases, it is postulated as being at 1.2%. These stipulations allow us to estimate methane emissions from enteric fermentation per kilogram of hogs (kgCH₄/kg) for each factory’s fattening and breeding pigs. However, aligning the derived emission factors from Shaanxi Province with the benchmarks set by the Intergovernmental Panel on Climate Change (IPCC) necessitates an estimation of the annual CH₄ production for each fattening and breeding swine. Given the breeder pigs’ one-year breeding cycle, an aggregate of various production stages suffices. Yet, for the fattening pigs, with an average cycle of 160 days, extrapolation to an annual framework becomes imperative.

Table 11. Emission factors of methane from enteric fermentation of pigs on each farm.

Enteric Fermentation Methane Emissions	Pig Fattening kgCH4/kg	Pig Fattening kgCH4/Heads/Year	Pig Breeding kgCH4/kg	Pig Breeding kgCH4/Heads/Year
Pucheng New Six Technology	0.01122	2.69212	0.02419	2.90270
Baoji Zhengneng Farming	None	None	0.02527	3.03233
Baoji Zhenghui Farming	0.00887	2.54434	None	None

elucidates these calculations in detail.

Interestingly, the IPCC guidelines, recognizing pigs as non-ruminants, classify their enteric fermentation as a non-pivotal emission source. Consequently, prevailing research predominantly adopts the emission factor’s default value, segmented by a nation’s developmental index. This results in developed nations bearing an emission factor of 1.5 kgCH₄/head/year, whilst their developing counterparts have an emission factor of 1.0 kgCH₄/head/year. However, with diverse variables such as feed composition, pig genotype, breed, and breeding cycle, this demarcation appears overly generalized and misaligned with present-day nuances.

A review of the emission factors detailed in

Table 12. Calculation of carbon dioxide production from total energy consumption on farms.

Company Identification	Pucheng New Six Technology	Baoji Zhengneng Farming	Baoji Zhenghui Farming
Total purchased electricity KWh/year	1,387,000	1,406,511	941,172
Energy consumption CO2 emissions kgCO2/KWh	123,748.14	1,254,889.11	839,713.66
Carbon dioxide produced per pig per year kgCO2	none	234.12	73.02

reveals that, broadly speaking, the current methane emission factor from enteric fermentation of swine in Shaanxi Province’s major pig farms surpasses the default thresholds stipulated by the IPCC. This underscores a prevalent underestimation of methane emissions from this source in the province, when benchmarked against the IPCC’s baseline values. Across the surveyed enterprises, the mean emission factor for fattening pigs stood at 2.61823 kgCH₄/head/year, whereas for breeding pigs, it was 2.96752 kgCH₄/head/year. Notably, enteric fermentation methane emissions from breeding swine of a consistent breed surpassed those from fattening pigs, potentially attributable to variations in feed composition and intake dynamics.

3.4. CO₂ Emissions from Farm Energy Consumption

In a detailed analysis of energy consumption across the three aforementioned farms, it was discerned that the principal energy expenditure stemmed from procured electricity. Thus, direct carbon dioxide emissions attributable to chemical energy sources, like coal and petroleum, were overlooked. Instead, emphasis was placed on calculating the indirect carbon dioxide emissions from electricity consumption, utilizing the previously delineated formula. The findings from this computation are comprehensively displayed in Table 12.

Given the dual nature of Pucheng Xinliu Science and Technology’s breeding operations—comprising both fattening and breeding pigs—the quantification of average annual carbon dioxide emissions per pig was sidestepped. However, the data collated in Table 12 reveal a striking contrast: breeding pigs emit an average of 234.12 kgCO₂ annually, markedly surpassing the 73.02 kgCO₂ attributed to fattening pigs. A plausible explanation for this pronounced disparity lies in the breeding pigs’ distinct rearing process. The heightened demands for specific environmental parameters such as temperature and humidity during various growth stages of breeding pigs necessitate the intensified activity of environmental control apparatus, consequently leading to augmented electricity consumption.

3.5. Calculating Methane Emissions from Manure Management

Utilizing the formula presented and referencing the IPCC guidelines for computation, it is imperative to initially ascertain the value of MCF_i,j in Equation (8). As per extant research [7], the Shaanxi region predominantly falls within the medium-temperature category. This categorization, in conjunction with the pertinent IPCC indicators, facilitates the determination of the default value for MCF_i,j, which is systematically illustrated in

Table 13. Default values of the methane conversion factor for different manure management practices.

Manure Management Practices	Oxidation Pond	Fuel Combustion	Solid Storage	Uncovered Anaerobic Pond	Compostable	Direct Fertilization	Fermenter
MCF (%)	71	10	4	77	0.8	0.5	10

.

The IPCC-derived default values play a significant role here. Given that the swine breeds under consideration are imports and their feeding regimen parallels that of more industrialized nations, a default value of 0.45 m³CH₄/kg, associated with developed countries, was adopted. A concise overview of manure management strategies employed by the three firms is depicted in Figure 3. As detailed in Figure 3, Pucheng Xinliu Science and Technology primarily harnesses composting (90%) and fermentation (10%) as its manure treatment modalities. Conversely, Baoji Zhengneng Farming predominantly utilizes manure for in-house agricultural applications, while Baoji Zhenghui Farming’s approach leans heavily towards composting.

Figure 4 enumerates methane emission factors, bifurcated by distinct manure treatment practices, for both fattening and breeding swine across the involved establishments. A comparative analysis of Figure 4 highlights that the methane emissions resultant from the field application treatment method in Pucheng Xinliu are considerably lower than those from composting. Furthermore, fattening pigs under Pucheng Xinliu’s purview exhibit a higher methane emission factor compared to Baoji Zhengneng Nongmu. This can be attributed, in part, to Pucheng Xinliu’s extended fattening cycle and the elevated methane output associated with fermentative treatments compared to composting. It is therefore recommended that farms recalibrate their strategies, accentuate the field application of manure, and advocate for an integrated crop-livestock model, thereby mitigating methane emissions during this phase. For large-scale pig farms, the adoption of integrated crop-farming systems offers a significant opportunity to mitigate greenhouse gas emissions. Key to this approach is the expansion of land allocated for waste elimination, coupled with the optimization of manure treatment processes. By enhancing the efficacy of manure return treatments, these farms can effectively utilize organic fertilizers to bolster soil nutrient content. This, in turn, facilitates more efficient feed production. Such a holistic strategy not only contributes to the reduction in emissions from large-scale pig farming operations but also embodies a sustainable approach to agricultural practice, marrying waste management with crop cultivation in a manner that benefits both the environment and farm productivity.

3.6. Calculating Nitrous Oxide Emissions from Manure Management

According to the IPCC guidelines, indirect N₂O emissions encompass emissions resulting from N volatilization as well as those originating from nitrogenous losses via leachate runoff. Notably, the agri-businesses within the study region have implemented leachate collection and remediation systems on their properties to mitigate the manure-induced contamination of adjacent soil. Consequently, this research excludes indirect emissions attributed to leaching and runoff, reflecting the on-ground practices. A pivotal variable essential for calculating N₂O emissions stemming from swine manure management is denoted as $B_{N_{2}O}$.

Table 14. Nitrous oxide production capacity per kilogram of manure for hogs.

Manure Management Practices	Compostable	Direct Fertilization	Fermenter
${\mathrm{B}}_{{\mathrm{N}}_2\mathrm{O}}$	0.006	0.005	0.006

systematically presents the nitrous oxide production potential per kilogram of hog manure, as stipulated by the IPCC.

Using the aforementioned formula, the daily N₂O yield across varied growth phases of fattening and breeding swine under distinct manure treatment regimes can be derived. The computation outcomes are consolidated in Figure 5. Analysis reveals that the N₂O production from manure during the lactation phase of breeding hogs markedly surpasses that of other growth intervals. Moreover, within a single enterprise, the N₂O generation potential during the fattening, reserve, and gestation periods of breeding pigs remains relatively consistent, possibly owing to analogous feed consumption patterns during these stages. A comparative assessment across different firms indicates that N₂O emissions resultant from field application treatments are inferior to those from composting and fermentation tanks across diverse growth stages. This observation reinforces the prior conclusion advocating for farms to judiciously select manure treatment methodologies and amplify their integrated farming and consumption practices.

3.7. Estimation of Carbon Emissions from the Hog Industry in Shaanxi Province

Upon analyzing the data across the three distinct farming enterprises, discernible disparities in carbon emissions associated with hog rearing become evident. These disparities arise due to variances in breeding strains, feeding practices, and manure treatment approaches employed by each enterprise. This study seeks to explore potential shifts in the total carbon footprint of Shaanxi Province’s hog sector if the feeding strategies of the aforementioned firms were universally adopted as the industry’s benchmark operational mode. Based on the preceding analysis, both Baoji Zhengneng Farming and Baoji Zhenghui Farming focus singularly on breeding or fattening pig rearing stages. Given the marginal discrepancies in their breeding strains and management strategies, they are collectively conceptualized as a unified production framework, referred to as the “Baoji model”, setting the stage for comparison against the “Pucheng model”.

Carbon emissions across these models were calculated, converting disparate greenhouse gas emissions at each production juncture into their CO₂ equivalents. Under the Pucheng model, a single fattening pig registers carbon emissions of 328.5283 kg, whereas a breeding pig contributes 539.2060 kg. Conversely, the Baoji model yields emissions of 249.2897 kg for fattening pigs and 551.6733 kg for breeding pigs. Notably, the Baoji model exhibits reduced carbon emissions for fattening pigs but marginally elevated emissions for breeding pigs compared to the Pucheng model. Drawing from the 2022 Shaanxi Provincial Statistical Yearbook, the 2021 provincial pig stock stood at 8,853,000, including 851,000 breeding hogs. Utilizing both management paradigms, carbon emissions for the entire hog sector in Shaanxi were calculated, and projections were provided for potential future emissions contingent upon varying output levels, with Figure 6 and Figure 7 being obtained.

As illustrated in Figure 6 and Figure 7, employing the Pucheng model would lead to carbon emissions from fattening pigs amounting to 262.9 × 10⁷ kg in 2021, while breeding pigs would account for 45.9 × 10⁷ kg. In contrast, under the Baoji model, these figures adjust to 199.5 × 10⁷ kg and 46.9 × 10⁷ kg for fattening and breeding pigs, respectively. For fattening pig operations, the Baoji model proves environmentally superior, whereas for breeding pig operations, the Pucheng model is more carbon-efficient. This underscores the imperative for tailored management strategies contingent upon the specific hog strains and rearing phases. Additionally, Figure 6 and Figure 7, benchmarked against the 2021 provincial pig production, project total carbon emissions under potential future production scenarios, fluctuating by 5% and 10%. Such projections underscore the environmental advantage of curtailing fattening pig production, as it significantly diminishes the overall carbon footprint of the provincial hog sector, without compromising supply security.

4. Conclusions

Based on the related studies and directives from the IPCC, this study offers a detailed overview of greenhouse gas emission accounting specific to hog farming operations. Utilizing the life cycle assessment approach, this research work delineates the entire process of hog farming, encompassing feed production, processing, transportation, and even the upstream facets of the farming chain. Emphasis is laid on understanding various emission facets: methane from pig enteric fermentation, methane and nitrous oxide from manure management, emissions from feed production to transportation, and emissions arising from farm-based energy consumption. Through these varied emission sources, this study provides an exhaustive evaluation of the greenhouse gas footprints associated with the pig farming ecosystem. This work seeks to deliver a holistic and systematic methodology, advancing the goal of sustainability, green development, and reduced carbon footprints in pig farming. The main conclusions are as follows:

(1)

Greenhouse gas emissions from feed production, processing and transportation. The cultivation and processing of primary feed components—corn, soybean meal, and wheat bran—play a pivotal role in the overall greenhouse gas emissions of the hog farming supply chain. Through comparative analysis, data from Pucheng Xinliu Science and Technology, Baoji Zhengneng Farming, and Baoji Zhenghui Farming and Animal Husbandry indicate that for each kilogram of pork produced, the CO₂ emissions from feed cultivation amount to 0.68777 kg, 1.19164 kg, and 0.60742 kg, respectively. Notably, CO₂ emissions linked to corn and wheat feed production are significantly higher compared to soybeans. A detailed vertical assessment of feed production underlines the pronounced contribution of electricity used in irrigation and drainage, along with nitrogen fertilizer inputs, to the total CO₂ emissions. Targeting these areas is thus essential for achieving agricultural carbon reduction objectives. Furthermore, when examining the transportation aspect of feed, CO₂ emissions per kilogram of pork produced were found to be 0.11521 kg, 0.33274 kg, and 0.20624 kg for Pucheng Xinliu Technology, Baoji Zhengneng Farming, and Baoji Zhenghui Farming, respectively.

(2)

Enteric fermentation methane emissions from pig rearing. In the assessment of large-scale pig farms in Shaanxi Province, the emission factor for enteric fermentation methane in live pigs exceeds the Intergovernmental Panel on Climate Change (IPCC) default values, suggesting a potential underestimation in the region’s methane emission metrics as per the IPCC standards. Detailed analyses indicate an average methane emission factor of 2.61823 kgCH₄/head/year for fattening pigs. For breeding pigs, this value rises to 2.96752 kgCH₄/head/year. Intriguingly, within identical genetic strains, breeding pigs manifest elevated enteric methane emissions compared to fattening pigs.

(3)

Farm energy consumption CO₂ emissions. In Shaanxi Province, pig farming operations primarily rely on electricity, which powers essential management tasks such as sanitation, illumination, and climatic adjustments. Our analysis reveals that breeding pigs contribute to annual carbon dioxide emissions of 234.12 kgCO₂ each, notably surpassing the 73.02 kgCO₂ attributed to fattening pigs. This discrepancy is likely due to the elevated environmental standards—such as temperature and humidity—demanded during the breeding stages. As a result, breeding pigs necessitate more intensive use of environmental control systems, leading to higher electricity consumption.

(4)

Methane emissions and nitrous oxide emissions from manure management. Upon consolidating data from three pig farms, we observed that during the nursery phase, fattening pigs contributed an average of 0.01924 kg CH₄ per head daily, while during their fattening period, the methane emission surged to 0.28111 kg per head daily. For breeding pigs, methane emissions across various stages were as follows: fattening, 0.03391 kg; nursery, 0.18583 kg; reserve, 0.09884 kg; gestation, 0.20223 kg; and lactation, 0.62378 kg per head daily. In terms of nitrous oxide (N₂O) emissions, during the nursery and fattening phases of fattening pigs, the emissions were 0.00087 kg and 0.00294 kg per head daily, respectively. For breeding pigs, the N₂O emissions across stages were as follows: fattening, 0.00130 kg; nursery, 0.00267 kg; reserve, 0.00267 kg; gestation, 0.00289 kg; and lactation, 0.00706 kg per head daily. It is worth noting that within a singular enterprise using consistent manure treatment methods, the methane and nitrous oxide emissions from breeding pigs during the fattening, reserve, and gestation phases were comparable. Significantly, the daily methane and nitrous oxide emissions from lactating pigs markedly surpassed those from other stages of rearing.

(5)

Our study assessed carbon emissions from pig breeding, contrasting the Pucheng and Baoji models, and subsequently quantified the cumulative carbon footprint of Shaanxi’s swine sector. Under the Pucheng model, the carbon emissions for fattening and breeding pigs were determined to be 328.5283 kg and 539.2060 kg, respectively. When carrying out this model across the province in 2021, it is projected to result in carbon emissions of 2.629 × 10⁹ kg for fattening pigs and 4.59 × 10⁸ kg for breeding pigs. Conversely, the Baoji model exhibited a carbon footprint of 249.2897 kg for each fattening pig and 551.6733 kg for each breeding pig. With province-wide adoption of the Baoji model in 2021, the estimated emissions for fattening pigs would decrease to 1.995 × 10⁹ kg, whereas breeding pigs would witness a marginal rise to 4.69 × 10⁸ kg. Critically, maintaining consistent supply levels while decreasing fattening pig production could play a pivotal role in substantially curtailing the carbon emissions of the swine sector in Shaanxi Province.

5. Discussion

In this research, we computed the total life cycle carbon emissions of pig production under both the Pucheng and Baoji models. Our findings indicate that the average carbon footprint (CF) of large-scale pig farms in China is approximately 3.6281 kgCO₂/kg of pork. This value is significantly lower than that observed in smallholder free-range models within the same regional context, amounting to just 53.7% of the latter’s emissions [6]. This disparity underscores the potential environmental benefits of transitioning towards large-scale pig farming in developing countries with contexts similar to China. Such a shift would leverage the management efficiencies of large-scale operations, promoting green and low-carbon development within the industry. Furthermore, our study reveals that the average CF of large-scale pig farms in China is marginally higher than those in France [35] and Sweden [36], yet comparable to large-scale organic farms in the Netherlands and Denmark [37]. This comparison suggests that China’s recent efforts to achieve green development in hog farming are yielding positive results. The prevalent model in Chinese large-scale hog farms, which integrates breeding with crop production and combines planting and breeding, appears to be both green and effective. This approach enhances waste utilization in the hog industry, converting waste into organic fertilizer to improve soil quality. Improved soil conditions subsequently benefit feed production, thereby contributing to a reduction in the overall CF. Such synergies between waste management and agricultural practices not only demonstrate the effectiveness of China’s strategies in the sector but also provide valuable insights for sustainable practices in global pig farming.

In the related carbon emission studies on pig systems, methodologies have varied, encompassing macro-level life cycle analyses [33], meso-level qualitative studies [26], and micro-level empirical measurements [7]. Despite the diversity of these approaches, an integrative method combining life cycle analysis, economic coefficients, and empirical measurements grounded in actual production data remains underexplored. In particular, many studies have transposed formulas developed under European conditions to Chinese contexts without adjustments, potentially leading to biased estimates and limited applicability to large-scale farms in developing countries. Our study addresses this gap by amalgamating life cycle formulae and segmenting pig production into detailed stages, including both breeding and fattening phases. We selected three pig farms emblematic of large-scale production in China, characterized by management methods and models reflective of the prevalent Chinese agricultural framework. Our research synthesizes current feeding patterns in China’s large-scale hog farming industry, providing a relevant empirical base that may be adapted to diverse international contexts. This work offers a methodological advancement for accurately measuring carbon emissions in large-scale farming operations, specifically tailored to the developing world. The adaptability of our proposed measurement formula across different management patterns in varying countries and regions underscores its potential as a universal tool for assessing and mitigating the environmental impact of large-scale agricultural enterprises.

Future studies in this field ought to expand their scope by meticulously selecting a diverse range of typical large-scale farms across different regions for field research. A geographical approach, particularly within Shaanxi Province, could be applied to segment the province into distinct zones such as northern Shaanxi, Guanzhong, and southern Shaanxi. This division would facilitate a comprehensive vertical analysis of the impact of geographic characteristics on greenhouse gas (GHG) emissions from hog farming systems across these varied regions. Additionally, a horizontal comparison within the same regions could examine how different management practices and hog breeds influence GHG emissions. To further refine the accuracy of this research, detailed investigations into the feed ratios for different hog breeds and growth stages are essential. This would necessitate the development of a more standardized and precise questionnaire aimed at quantifying GHG emissions from the entire lifecycle of hog farming feed, including its production, processing, and transportation. Such methodological advancements would significantly enhance our understanding of the environmental impact of hog farming practices, providing valuable insights for the development of more sustainable agricultural strategies.

6. Policy Recommendations

This study underscores the progress achieved in the green, carbon-reducing production models of large-scale pig farming enterprises in China, highlighting the industry’s high performance levels. However, it also identifies key areas for environmental sustainability improvements. The feed production stage, characterized by significant CO₂ emissions due to drainage and irrigation electricity consumption and nitrogen fertilizer usage, is a primary focus for achieving agricultural carbon reduction goals. This necessitates a shift towards greener and low-carbon feed production practices, particularly pertinent for developing countries aiming to advance the overall green development of pig farming. Moreover, the model employed by large-scale pig farming enterprises presents a viable template for broader industry adoption. Governments in developing nations are encouraged to steer small-scale pig farmers towards more specialized and large-scale operations. This transition should leverage the advanced production models of large-scale enterprises, fostering an organic synergy between “company + farmer” pig production models, thereby catalyzing the green transformation of the entire live pig industry. Large-scale farms, in adapting to their specific contexts, should enhance waste management by expanding land allocation for waste elimination and implementing integrated crop-farming models. This approach, along with optimizing manure treatment processes and utilizing organic fertilizers to improve soil nutrients, can significantly reduce greenhouse gas emissions while boosting efficient fodder production. Furthermore, given the regional variations in feed supply, transportation methods, and manure management within the hog farming industry across different countries, large-scale farming enterprises should tailor their data collection and analysis to reflect actual feed components and hog production practices. Developing countries are encouraged to establish long-term sentinel observation of greenhouse gases (GHGs) in large-scale aquaculture enterprises and promote the accumulation of data on GHG emission levels and factors. This comprehensive data collection is essential for analyzing regional carbon footprints and developing targeted emission reduction strategies.