Mitigation of Enteric Methane Emission from Dairy Animals in India Through Nutritional Intervention
Dr Nilufar Haque1 & Dr Sk Asraf Hossain2
1Assistant Director of Extension, Directorate of Research, Extension & Farm, WBUAFS, Kolkata, West Bengal-700037
2Veterinary Officer, Additional Block Animal Health Centre, Chanchal-II, Malda, West Bengal-732139
*Corresponding author: haquenilufar@gmail.com
Abstract:
Enteric fermentation in livestock is an important source of anthropogenic methane emission. Ruminants fed on low-quality feed/fodder produce over 75% of the CH4 generated by ruminants worldwide. Therefore, strategies regarding enteric methane mitigation with practical and sustainable approaches, suitable for Indian feeding and management conditions are highly needed. Most of these strategies are inept for long term mitigation options because of their limitations. Further, many of these strategies require years of research before practical application and until commercially viable products are available. In addition, the environmental impacts of strategies should also be taken into consideration. Studies suggest that improving animal productivity through balanced feeding could be a most practical and sustainable way to mitigate methane emission from ruminants in India. Planned nutritional intervention to improve digestive efficiency in these animals could halve this CH4 production. Although some CH4 abatement strategies have shown efficacy in vivo, more research is required to make any of these approaches pertinent to modern animal production systems.
Keywords: Methane Emission, mitigation strategies, productivity, ruminants, dairy animals, balanced nutrition
Background
Methane (CH4) is a hydrocarbon and the chief component of natural gas. Methane is also a potent and plentiful greenhouse gas (GHG), which makes it a remarkable contributor to climate change, especially in the near term. Methane is emitted during the production as well as transport of coal, natural gas, and oil. Emissions also result from livestock and other farming practices and from the decompose of organic waste in municipal solid waste landfills and certain wastewater treatment methods. Enteric fermentation is the key source of CH4, accounting for 90% of total CH4 emissions. Large ruminants, specially cattle and buffalo are responsible of releasing hefty quantities of CH4.
Although impacting environment, livestock is and will continue to remain a livelihood choice for millions of rural poor in India. Being the largest milk producer and consumer in world, India has the largest livestock population, accounting for ~50% of total CH4 emissions in India (INCCA, 2007). In view of considerable impact of methane (CH4) on climate change, there has been rising interest in the scope for mitigating CH4 emissions from ruminants. Hence, there is a growing consciousness among the researchers for superior nutrition of large ruminants, especially in developing countries, for implementing feeding strategies for eco-friendly animal production system (Singh G P and Mohini M, 1999).
Enteric methane
Enteric CH4 is formed as a result of microbial fermentation of feed components. Fermentation of feeds in the rumen is the major source of CH4 from enteric fermentation and is mainly emitted from the animal by eructation. The conversion of feed material to CH4 in the rumen involves the integrated activities of different microbial species, with the final step carried out by methanogenic bacteria (Fig. 1).
Fig. 1 Methane formation in rumen
Hydrogen – a central regulator of rumen fermentation
Hydrogen for CH4 synthesis occurs in 3 main states in the rumen, these are
- hydrogen gas,
- reduced cofactors (such as NADH and NADPH), and
- as free protons.
Hydrogen in all its forms is a vital regulator of rumen fermentation and for this reason, it has been referred to as the “currency” of rumen fermentation.
Although H2 is one of the most important end products of fermentation by protozoa, fungi and pure monocultures of some bacteria, it does not accumulate in the rumen because, it is immediately utilized by other bacteria, which are there in the mixed microbial ecosystem. In the rumen, formation of CH4 is the major way of H2 sink through the reaction: CO2 + 4H2 → CH4 + 2H2O. H2 sinks in the rumen are shown in Fig. 2.
Fig.2 Emission and sink of Hydrogen in rumen
Literature affirms that the management of H2 production in the rumen is the most significant factor to be considered when developing strategies to control ruminant CH4 emissions. It should therefore be possible to lessen CH4 production by inhibiting H2 liberating reactions or by promoting alternative H2-using reactions or routes for disposing of H2 during fermentation.
Need of reduction of enteric CH4 emission
Enteric CH4 emission means a loss of energy to the production system, as fraction of the energy consumed as feed is lost in the form of CH4 instead of being assimilated by animals and used for production. Cattle can generate 250-500 litre of CH4 per day and enteric fermentation causes 2–12% loss of dietary gross energy (GE) intake as CH4 in ruminants (Johnson KA and Johnson DE, 1995). Thus, it is the need of hour to decrease the share of CH4 from ruminants to environmental pollution and make use of this energy of food for benefit of the host animal.
Measurement of enteric methane
Selection of technique to measure CH4 emission from ruminants is paramount important. Different techniques used to determine CH4 from animals have been reported. These comprise the use of respiration calorimetry chambers, isotopic technique, sulphur hexafluoride (SF6) tracer technique, in-vitro gas production technique and mass balance/micrometeorological techniques. Based on the advantages and disadvantages of diverse available techniques, it has been seen that, for measurement of CH4 emissions from huge number of ruminants under natural conditions of feeding and management, SF6 tracer technique proves to be a more trustworthy technique, as compared to others. It is widely applied, economic and only viable method with minimum disturbance of animals under field conditions.
Methane mitigation strategies
Following are few strategies focusing mainly on feeding, breeding and rumen manipulation.
A) FEEDS AND FEEDING MANAGEMENT
Following feeds and feeding management practices be expected to have a positive role in improving feed use efficiency and lowering CH4 emissions in ruminants.
i) Feed intake
Feed intake is an main variable in predicting CH4 emission. Johnson KA and Johnson DE (1995) noted that, CH4 loss as percent of GE intake declined by 1.6% units for each multiple increase of intake. This is caused mainly by the rapid passage of feed out of the rumen. As a result of the increased passage rate, the extent of microbial access to organic matter (OM) is decreased, which in turn reduces the extent and rate of ruminal dietary fermentation. Also, a rapid passage rate favors propionate production, which is a competitive pathway for the use of hydrogen.
ii) Feeding frequency
Low frequency of feeding tends to increase propionate production, reduce acetic acid production and lower CH4 production in dairy animals. This is mainly due to the lowering of methanogens as a result of high fluctuations in ruminal pH, since low feed frequencies increase diurnal fluctuations in ruminal pH that can be inhibitory to methanogens (Shabi et al., 1999).
iii) Feed processing
Processing, through its effect on digestibility, energy losses and passage rate, can be an effective CH4 mitigation strategy. Grinding to improve the utilization by ruminants has been shown to decrease CH4 losses per unit of feed intake (Johnson et al, 1996). The lowered fibre digestibility, decreased ruminally available organic matter (OM) and faster rate of passage associated with ground forages can also explain the decline in CH4 production. However, application of this strategy in Indian feeding and management conditions is insignificant.
iv) Inclusion of concentrates
Increasing the ratio of concentrate in the diet reduces CH4 emissions per unit of feed intake and animal product. The addition of grain to forage diet enhance starch and reduces fibre intake, reducing the rumen pH and favouring the production of propionate rather than acetate in the rumen (McAllister TA and Newbold CJ, 2005).
v) Forage quality
Improving forage quality tends to enhance the voluntary intake and decreases the retention time in the rumen, promoting energetically more efficient post-ruminal digestion and reducing the proportion of dietary energy converted to CH4. For feeds with higher digestibility, increased dry matter intake (DMI) depresses the amount of CH4 produced per unit of feed consumed (Hammond et al., 2013). Methane emissions are also generally lower with higher proportions of forage legumes in the diet, partly because of the lower fibre content, the faster rate of passage, and in some cases, the presence of condensed tannins. Improving forage quality, either through feeding forage with lower fibre and higher soluble carbohydrates, changing from C4 to C3 grasses, or even grazing on less-mature pastures, can reduce CH4 production (Ulyatt et al., 2002).
vi) Feeding of balanced ration
Improving productivity and efficient use of nutrient through balanced nutrition is also one of the most promising ways to reduce CH4 emissions in dairy animals. Animals fed imbalanced ration not only produce less milk at a elevated cost, but also produce more CH4 per litre of milk (Sherasia et al., 2016). For this reason, improving animal productivity and reducing CH4 emissions from livestock in developing countries can be achieved through proper diet formulation. Balanced feeding have an indirect effect on enteric CH4 emission through maintaining a healthy rumen and maximizing microbial protein synthesis, which is important for maximizing feed efficiency and decreasing CH4 per unit of milk.
Rationale for reducing CH4 emissions through balanced feeding
- Microbial N supply
Microbial N supply to the duodenum is an vital indicator of efficiency of rumen function. Supply of adequate nutrients increases excretion of urinary purine derivatives, synthesis of rumen microbial N and enhances the supply of protein post-ruminally to support production (Makkar HPS and Chen XB, 2004). A deficiency of feed N leads to spillage of ATP released on digestion of feed C and suboptimum synthesis of microbial protein and release of feed C as CH4.
- Electron sink
Methane is the chief electron sink in ruminal fermentation. Methanogens act as an essential electron sink for all microbes, thereby maintaining a low partial pressure of H2 in the rumen which in turn promotes maximal production of ATP to maintain microbial growth. It would be beneficial both for the efficiency of production and the environment to divert reducing equivalents from ruminal methanogenesis into alternative electron sinks with a nutritional value for the host animal, e.g., by enhancing propionate formation (Fig. 3).
Fig. 3 Rationale for reducing CH4 emissions through balanced feeding
vi) Feed Additives
A variety of feed additives are available in the market, having direct or indirect effect on reducing CH4 emissions in cattle and buffaloes. Some of the commonly used such feed additives are given below.
a) Ionophores
Ionophores, which are added to ruminant diets to enhance the efficiency of feed utilization, have been shown to decrease CH4 production. Monensin is the most frequently used and studied ionophore, with others such as lasalocid, tetronasin, lysocellin, narasin, salinomycin and laidomycin. Monensin reduces the acetate to propionate ratio in the rumen, effectively reducing CH4 production. However, with the rising public and health authorities concerns on the use of chemical or antibiotic feed additives in animal production, the use of ionophores to mitigate CH4 production might not be the conceivable strategy.
b) Probiotics
A little information on the effects of probiotics on CH4 production in dairy cattle is available. It has been proposed that probiotics give nutrients, including metabolic intermediates and vitamins that encourage the growth of ruminal bacteria, resulting in improved bacterial population. Probiotics is also indicated to stimulate lactic acid utilizing bacteria, resulting in a reduction of lactic acid and a more stable ruminal environment. A less acidic ruminal environment favours the growth of cellulolytic bacteria, which in turn improves fibre digestion, feed intake, and production response. In vitro study on effect of supplementing most widely used probiotics like Saccharomyces cerevisiae and Aspergillus oryzae shown to reduce CH4 production in the range of 10-50% (Mutsvangwa et al., 1992). However, there is a need for further research to establish the potential of probiotics for reducing CH4 production in-vivo.
c) Enzymes
Recently, some enzymes are shown to increase feed efficiency in dairy cows and reduce methane (Holtshausen et al., 2011). It is reported that when the enzymes are added to the diets of ruminants, in the form of cellulases and hemi-cellulases, they improve ruminal fibre digestion, productivity and reduce CH4 production, perhaps by reducing the acetate-to-propionate ratio.
d) Direct methane inhibitors
Chemical compounds like bromochloromethane, 2-bromoethane sulfonate, chloroform, and cyclodextrin are potent inhibitors of CH4 formation in ruminants. These inhibitors can reduce CH4 production by up to 50% in-vivo (Mitsumori et al., 2011). Reduction of protozoal numbers has been shown to reduce CH4 production.
e) Propionate enhancers
Dicarboxylic acids like fumarate, malate, and acrylate, are precursors to propionate production in the rumen and can act as an alternative H2 sink, restricting methanogenesis. Nitrate can also replace CO2 as an electron acceptor, forming ammonia as an alternative H2 sink in the rumen. However, due to relatively high doses required, these compounds are prohibitively expensive as a mitigating strategy.
f) Secondary plant metabolites
There is a growing interest in exploiting secondary plant metabolites as feed additives to manipulate enteric fermentation and possibly reduce CH4 emissions from livestock production. Essential oils, tannins and saponins have been extensively studied in this category.
- Essential oils
Essential oils are present in many plants and may have antimicrobial properties, which have been shown to control fermentation gases. Benchaar C and Greathead H (2011) suggested that some essential oils e.g., garlic and its derivatives and cinnamon, reduce CH4 production in vitro. However, these compounds have not been studied extensively in vivo, and there is no evidence that they can be used successfully to inhibit rumen methanogenesis.
- Tannins and saponins
Tannins, as feed supplements have shown a potential for reducing CH4 emission by up to 20%. Though, it is important to note that the benefits of reduced CH4 yields should not overshadow detrimental effects of tannins on digestion and production. Plant saponins also potentially reduce CH4 and some saponin sources are clearly more effective than others, with CH4 suppression attributed to their anti-protozoal properties (Zhou et al., 2011). Although extracts of condensed tannins and saponins are commercially available, their cost is currently prohibitive for routine use in ruminant production systems.
B) RUMEN MANIPULATION
Manipulating microbial populations in the rumen through chemical means or with vaccination can reduce CH4 production.
i) Defaunation
Defaunation has been shown to decrease CH4 production by about 20 to 50%. Reduced ruminal methanogenesis observed with defaunation can be attributed to factors such as a shift of digestion from the rumen to the hind gut or the loss of methanogens associated with protozoa during defaunation. It has been reported that the complete elimination of protozoa is not recommended as a method for reducing CH4, as it depresses fiber digestion. On the other hand, protozoa have been reported to negatively influence ruminal protein metabolism through predation of bacteria, which reduces the flow of microbial protein leaving the rumen (Koenig et al., 2022). Therefore, the exercise of defaunation to mitigate CH4 production from ruminants should be weighed against its possible impact on the efficiency of the whole ruminal system.
ii) Vaccination
The development of a vaccine against cell-surface proteins common to a broad range of methanogen species may develop the efficacy of vaccination as a CH4 mitigation strategy. Vaccines against archaea have been successful in-vitro (Wedlock et al., 2010) but not in-vivo (Williams et al., 2009). Wright ADG and Klieve AV (2011) explained that the vaccination may be used as an effective CH4 mitigation strategy in the future, following extensive research in this area.
iii) Ruminally produced bacteriocins and archaeocins
Similar to exogenous bacteriocins, there are bacteriocins released within the rumen itself and could represent a new type of rumen modifier. Bovicin, a bacteriocin produced by Streptococcus bovis has been reported as a possible CH4 mitigating agent in the rumen (Lee et al., 2002). Archaea, like bacteria, produce substances referred to as archaeocins that also inhibit microbial growth. Such biological control strategies could prove effective in directly inhibiting methanogens and redirecting H2 to other reductive rumen bacteria, such as propionate producers or acetogens (McAllister TA and Newbold CJ, 2012).
- C) BREEDING
- i) Animal breeding
An alternative to animal feeding is to selectively breed livestock having more feed conversion efficiency and lower CH4 production per unit DMI (Hegarty RS and McEwan JC, 2010). It is possible to select for reduced CH4 production indirectly via correlated traits such as feed intake or rumen digesta retention time.
ii) Plant breeding
Plant breeding can be expected to have a place in reducing livestock CH4 emissions but new species are still to be commercialized. Selecting plants for characteristics that change rumen conditions could include, for example, high sugar in perennial rye grasses or tannins. High sugar grasses might have shifted rumen fermentation towards higher proportions of propionate and butyrate (Lee et al., 2001), which may reduce CH4 production. However, extensive research and field trials need to require before commercial application of such varieties.
Need for collective and concerted action
In view of increasing interest in the scope for minimizing methane emissions from ruminant livestock, there is a need of society to have collective and concerted action in India. By involving all stakeholders like private and public sectors, civil societies, national research institutes, state agricultural universities and national organizations involved in livestock mediated methane emissions; the basic and practical approach i.e. feeding as per the nutrient requirement of animals can be used in different agro-climatic regions of the country. There is also need to focus on practice innovation, supported by knowledge transfer and awareness intensifying amongst the rural milk producers to achieve maximum milk production, thereby reducing CH4 emissions per unit of milk.
Conclusion
A number of CH4 mitigating strategies have been identified that can be implemented in animal production systems immediately or in near future, many of which are likely to be cost effective in their own right. Further, most of the strategies reviewed require many years of research before practical and commercially viable products and strategies are available for use. It is also clear that most of the strategies currently available are more suited to intensive animal production system, with far fewer strategies available for mixed crop-livestock feeding systems. For Indian feeding and management conditions, wherein most of the farmers follow traditional feeding practices using locally available feed resources, the CH4 mitigation strategy should be cost effective and also should address socio-economic issues. In this situation, balanced feeding confirms for improving productivity of dairy animals, by way of increasing nutrient use efficiency and there by reduces CH4 losses from ruminants. Therefore, optimizing rumen function for higher microbial protein synthesis through feeding a balanced ration, matching the physiological stage of an animal, and enhancing the overall efficiency of dietary nutrient use is the most efficient way of decreasing CH4 emissions per unit of milk. However, future research should be directed toward both the medium- and long-term mitigation strategies, which could be utilized on farms to accomplish substantial reductions of CH4.
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