Concerns about greenhouse gas (GHG) emissions from livestock and dairy farms, as well as their connection to global warming and climate change, have grown among the general public worldwide in recent years. Enteric methane (CH4) and other greenhouse gas emissions from ruminants can be mitigated in numerous ways.
1. Introduction
Carbon dioxide (CO
2) and methane are the two most important greenhouse gases, and since 1950, their concentrations in the atmosphere have increased from 350 to 410 ppm (a rise of 28%) and from 1100 to 1875 ppb (a rise of 70%), respectively
[1]. About 24% of worldwide methane emissions and a much greater fraction of anthropogenic methane emissions are related to the production of fossil fuels (coal, oil, and natural gas)
[2]. Human activities, including growing rice, keeping ruminant animals, using landfills and compost, treating wastewater anaerobically, producing natural gas, and mining coal, account for more than 60% of all CH
4 emissions. Wetlands and oceans account for the remaining 40% of methane emission
[3]. After livestock, rice cultivation is the largest source of methane. Flooded-field-grown rice emits twice as much greenhouse gas than wheat
[4]. Concerns have been raised in the realm of agricultural production regarding the effects that an increase in rice production may have on the surrounding environment, particularly regarding the emissions of greenhouse gases.Rice paddies are responsible for a significant amount of greenhouse gas emissions, specifically approximately 30 percent of all methane (CH
4) and 11–25 percent of all nitrous oxide (N
2O) emissions
[5]. Rice paddies are thought to be one of the largest human-made sources of carbon monoxide in the air, with an estimated 11% of all human-made CH
4 emissions coming from them
[6]. Linquist et al., in their study, found out that in terms of area, the global warming potential (GWP) of CH
4 and N
2O emissions from the rice paddies was much greater than that of wheat or maize
[7].
The agricultural sector is rapidly participating in greenhouse gas emissions. Globally in recent years, there has been a rising public concern about farm animals, dairy farms’ greenhouse gas emissions, and their impact on global warming and climate change
[8]. Research has found that increased CH
4 emissions can be substantially attributed to animal farming
[3]. Manure decomposition and microbial fermentation in the rumen produce methane, wherein the animal expels from the rumen via eructation
[9][10].
In terms of CO
2 equivalents, enteric fermentation and manure management emissions account for approximately 41% of agriculture’s overall GHG emissions
[11]. Emissions of greenhouse gases from milk production account for over 70% of all GHG emissions before the farm gate, with enteric CH
4 accounting for 35–55% of all farm emissions
[12]. According to the United States Environmental Protection agency, enteric fermentation expels about 27% of all US CH
4 emissions
[13] (
Figure 1). The investigation of nutritional and management strategies to minimize methane emissions is essential for long-term milk production
[14][15][16]. Dairy cow milk output has increased dramatically in recent years due to improved selection, feeding, and herd management approaches
[14]. Herbivores use their gut microbiota to convert fibrous feed resources into high-quality proteins (meat, milk) for human consumption
[17].
Figure 1. Source of US CH4 emissions in 2020.
A lot of study is ongoing to figure out how to reduce ruminant enteric methane emissions. There is no doubt that feeding contributes to methane release in dairy cattle, as it is produced during the digestion of high-fiber diets
[18]. Some mitigating strategies lower pasture digestion or feed consumption, which can affect feed conversion ratio and methane emissions per kilogram of product
[10]. A range of dietary management measures has been explored in order to lower enteric methane generation. Dropping diet forage to concentrate ratios, incorporating rumen modifications and methane antagonists like bromoform or other phytocompounds in the diet, or increasing dietary oil content are all nutritional alternatives for methane mitigation
[10][19][20]. A high-fiber diet can promote acetate production. The synthesis of acetate and butyrate is followed by the release of metabolic hydrogen, which has a deleterious impact on microbial development and on feed digestibility while accumulating in rumen fluid
[10][21]. Some food additives can be effective in the laboratory but not in reality
[22]. The use of naringin and chitosan positively affected fermentation patterns, increasing propionic acid while reducing acetate and methane production by 12% and 31%, respectively. Still, for the in vivo trial where chitosan and naringin were administered either separately or in a combination given directly into the rumen, both additives did not show a positive effect on rumen fermentation or enteric methane production
[22]. Other authors have studied seaweed‘s impact on methane emissions. Kinley et al. investigated
Asparagopsis taxiformis. The study showed in vitro that 20 g/kg of fodder with the mentioned algae almost completely abolished CH
4 generation while having no detrimental impact on forage digestibility
[23]. Using oil as a feed supplement also can give great expectations. Lipids can suppress methanogenesis by substituting rumen fermentable organic matter in the diet and by biohydrogenating unsaturated fatty acids, reducing the number of ruminal methanogens and protozoa
[24]. To meet future global demands, the livestock industry must investigate natural feed additives that improve nutrient utilization efficiency, provide antibiotic alternatives, and reduce ruminant methane emissions.
To evaluate methane emissions, there is a need to use reliable methods. Garnsworthy et al. compared various different methane measurement methods
[10]. In the research, methods like respiration chambers, the SF6 tracer technique, milking or feeding breath sampling, the GreenFeed
® (GF) system (C-lock Inc., Rapid City, SD, USA), and the laser methane detector were compared. The study’s purpose was to evaluate and compare the suitability of various technologies for measuring methane on the herd or individual animal level
[10]. When individual cows on commercial farms can be reliably measured directly for enteric CH
4, it allows for more focused emission mitigation. It also provides the potential for farm-level benchmarking and the selection of cows with low enteric CH
4 production. The use of mobile gas analyzers to detect CH
4 emissions from large numbers of animals across populations is of great interest
[9][10].
To slow climate change and lower greenhouse gas concentrations in the atmosphere, CH
4 emissions must be reduced. There is a need to perform more studies to find the most effective food supplement or its composition and contribute to reducing methane emissions without compromising animal health and production. This demands the use of low-cost and portable technologies for estimating CH
4 emissions on a wide scale while combining it with trustworthy forage
[25][26].
2. Role of Dairy Cattle in Global Warming
The atmosphere contains natural greenhouse gases such as carbon dioxide, methane, water vapor, and nitrous oxide (N
2O), as well as synthetic greenhouse gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), chlorofluorocarbons (CFCs), and sulfur hexafluoride (SF
6)
[13]. Agricultural systems are a substantial source of GHG emissions into the atmosphere, accounting for around 30% of total anthropogenic emissions, including indirect emissions through land-cover change, as CO
2, CH
4, and nitrous oxide are the three principal greenhouse gases released by animal production
[27]. Animal husbandry is a substantial source of GHGs, accounting for 14.5 percent of world emissions, which is roughly the same as the transportation industry
[28]. Ruminant livestock is expected to emit between 80 and 95 million tonnes of CH
4 per year globally
[29][30][31]. CH
4 generation also represents a loss of energy availability to the host ruminant animal, often accounting for between 2% and 12% of total energy availability
[25]. Cattle and sheep production systems contribute the most to GHG emissions in agriculture, accounting for up to 18% of total global GHG emissions, mostly in the form of enteric methane
[32]. Enteric CH
4 emissions from ruminant production are the most common source of greenhouse gases, accounting for 46 percent for dairy and 55 percent for small ruminant productions of total CO
2e emissions
[33]. Cattle are commonly mentioned among food-producing animals due to their significant contribution to the sector’s GHG emissions, particularly methane
[34]. The enteric fermentation process provides more than 90% of CH
4 emissions from livestock and 40% of agriculture GHG emissions
[35]. According to the Intergovernmental Panel on Climate Change and Food and Agriculture Organization of the United Nations—a fully developed cow can emit up to 500 liters of methane each day, which accounts for approximately 3.7 percent of all greenhouse gas emissions
[36]. Almost all the methane is formed in rumen while using protective mechanisms and released by burping. The rumen is a complex system comprised of elements like protozoa, bacteria, archaea, viruses, fungi, and bacteriophages, all of which contribute to the harvesting of food energy and subsequent provision of nutrients to the host. CH
4 is produced as a by-product of this fermentative process when hydrogen is liberated and used by methanogens to form CH
4 [37][38][39][40]. Rumen
Archaea are microorganisms that produce methane and water by combining metabolic hydrogen and carbon dioxide.
Archae also has a role in saving rumen from excess hydrogen by producing methane
[10]. The number of fiber fractions digested in the rumen is proportional to the rumen metabolism product amount. The more fiber content an animal digests, the more methane will be produced because of the acetate and hydrogen amounts in the rumen
[10]. That shows that the rumen environment can influence methanogen production
[15][41].
This entry is adapted from the peer-reviewed paper 10.3390/ani12192687