Strategies to Mitigate Enteric Methane Emissions from Ruminant Animals

Abstract

Ruminants are cloven-hoofed mammals of the Artiodactyla order, with domesticated cattle, sheep, and goats comprising 95% of the total ruminant population [14]. They obtain their food by browsing or grazing, subsisting on plant material using their specialized digestive system [15] with a sophisticated symbiotic web of microorganisms [16]. The digestive system of ruminants consists of four compartments -rumen, reticulum, omasum, and abomasum [17].In the rumen, the intricate community of bacteria (10 10 -10 11 cells/ml), ciliate protozoa (10 4 -10 6 cells/ml), methanogenic archaea (10 6 -10 8 cells/ml), and fungi (10 3 -10 6 cells/ml) synthesizes enzymes which breakdown complex macromolecules derived from feed [18,19]. This fermentative process produces short volatile fatty acids (SVFAs) and microbial crude protein, which is an essential source of energy and protein for the host, while the rumen provides the microbes a suitable environment for survival and growth [16,20]. Acetate (~65%), propionate (~20%), and butyrate (~15%) form the major part of SVFAs in the anaerobic rumen fermentation, which supplies 80% of the animal's total energy requirement [21]. Subsequently, methanogens in the gastrointestinal tract produce methane as a by-product of anaerobic fermentation [22].Human activities account for approximately two-thirds of global methane emissions, wherein the livestock sector is the single massive methane emitter. Methane is a potent greenhouse gas of over 21 times the warming effect of carbon dioxide. In the rumen, methanogens produce methane as a by-product of anaerobic fermentation. Methane released from ruminants is considered as a loss of feed energy that could otherwise be used for productivity. Economic progress and growing population will inflate meat and milk product demands, causing elevated methane emissions from this sector. In this review, diverse approaches from feed manipulation to the supplementation of organic and inorganic feed additives and direct-fed microbial in mitigating enteric methane emissions from ruminant livestock are summarized. These approaches directly or indirectly alter the rumen microbial structure thereby reducing rumen methanogenesis. Though many inorganic feed additives have remarkably reduced methane emissions from ruminants, their usage as feed additives remains unappealing because of health and safety concerns. Hence, feed additives sourced from biological materials such as direct-fed microbials have emerged as a promising technique in mitigating enteric methane emissions.

A newly developed strain of Enterococcus faecium isolated from fresh dairy products to be used as a probiotic in lactating Holstein cows

“…Moreover, the improved feed efficiency with the additives is another probable reason for the improved performance ( 41 ). As previously noted in Experiment 1, E. faecium decreased CH 4 production indicating that a possible suppression in CH 4 production would have redistributed energy for improved milk production ( 57 ). In this study, the antagonism of pathogenic organisms via antimicrobial effects, competition for adhesion sites or nutrients, stimulation of host defines mechanisms and inhibition of bacterial toxins can partially explain the improved milk production ( 9 , 45 ).…”

Different microbial genera drive methane emissions in beef cattle fed with two extreme diets

“…In 2019, methane levels in the atmosphere reached record levels, about 2.5 times higher than in the pre-industrial era. Ruminants account for 16% of global methane (CH 4 ) emissions, of which 35% and 30% correspond to beef and dairy industries ( Tseten et al, 2022 ). Methane is an unnecessary by-product of microbial fermentation of mainly complex carbohydrates in the rumen, synthesized by methanogenic archaea and released into the environment through the animal’s mouth and nose.…”

Innovations for Reducing Methane Emissions in Livestock toward a Sustainable System: Analysis of Feed Additive Patents in Ruminants

“…Ruminant livestock plays an important role in satisfying the increased demand of high biological value protein, as well as in terms of food safety and security, which could lead to improvements in human health and preservation of the environment [ 1 ]. Animal products, such as meat, milk, and eggs, are a source of essential nutrients such as heme-iron, vitamin B12, vitamin D3, zinc, calcium, and high-biological-value proteins characterized by high digestibility, containing all essential amino acids [ 2 ].…”

“…Thus, the reduction in ruminants’ enteric CH 4 , which is considered the most prevalent enteric emission in ruminants, is considered the most effective enhancement target in reducing global warming in the short term due to a lower atmospheric residence time value and greater power in heating the atmosphere than carbon dioxide [ 4 ]. Therefore, several mitigation strategies for reducing enteric CH 4 have been suggested, and a relevant number of extensive reviews are available on this issue [ 1 , 5 , 6 ], in which animals’ diet manipulations play a pivotal role [ 1 , 5 ]. CH 4 mitigation strategies could embrace different diet formulation approaches, e.g., adopting specific feed ingredients in animals’ diets such as protein, lipid, and forage–concentrate ratio, or supplementing specific dietary feed additives able to directly inhibit methanogens or alter metabolic pathways leading to reduced substrate for methanogenesis [ 7 , 8 ].…”