Methane production by ruminants: its contribution to global warming

Abstract

-The aim of this paper is to review the role of methane in the global warming scenario and to examine the contribution to atmospheric methane made by enteric fermentation, mainly by ruminants. Agricultural emissions of methane in the EU-15 have recently been estimated at 10.2 million tonnes per year and represent the greatest source. Of these, approximately two-thirds come from enteric fermentation and one-third from livestock manure. Fermentation of feeds in the rumen is the largest source of methane from enteric fermentation and this paper considers in detail the reasons for, and the consequences of, the fact that the molar percentage of the different volatile fatty acids produced during fermentation influences the production of methane in the rumen. Acetate and butyrate promote methane production while propionate formation can be considered as a competitive pathway for hydrogen use in the rumen. The many alternative approaches to reducing methane are considered, both in terms of reduction per animal and reduction per unit of animal product. It was concluded that the most promising areas for future research for reducing methanogenesis are the development of new products/delivery systems for anti-methanogenic compounds or alternative electron acceptors in the rumen and reduction in protozoal numbers in the rumen. It is also stressed that the reason ruminants are so important to mankind is that much of the world's biomass is rich in fibre. They can convert this into high quality protein sources (i.e. meat and milk) for human consumption and this will need to be balanced against the concomitant production of methane. methane / ruminants / global warning / reduction strategies Résumé -Production de méthane par les ruminants : sa contribution au réchauffement de la planète. Cet article examine le rôle du méthane dans le processus de réchauffement de la planète et évalue la contribution au méthane atmosphérique des gaz d'origine digestive issus principalement des ruminants. Les émissions annuelles de méthane d'origine agricole dans l'Europe des quinze ont été estimées récemment à 10,2 millions de tonnes et représentent la principale source des entrées Ann. Zootech. 49 (2000) 231-253 231 © INRA, EDP Sciences

Methane production and diurnal variation measured in dairy cows and predicted from fermentation pattern and nutrient or carbon flow

“…Although considered quantitatively unimportant (Morgavi et al, 2010), these alternative H 2 sinks might explain part of the residual variation. Moss et al (2000) assumed that 90% of the H 2 surplus produced during VFA production is recovered in CH 4 . However, adding a factor of 0.9 to equation (1) as proposed by Moss et al (2000) did not improve the prediction of CH 4 with the present data.…”

“…Moss et al (2000) assumed that 90% of the H 2 surplus produced during VFA production is recovered in CH 4 . However, adding a factor of 0.9 to equation (1) as proposed by Moss et al (2000) did not improve the prediction of CH 4 with the present data. In in vitro incubations, Demeyer (1991) found evidence that H 2 recovery might vary depending on substrate, as H 2 recovery rates from 76% to 98% were observed for soluble CHO.…”

“…Hydrogen recovered as CH 4 in the hind gut has been suggested to be substantially lower than in the rumen (Demeyer, 1991) and is estimated to be between 50% and 65% (Demeyer, 1991;Moss et al, 2000). According to Demeyer (1991), this can be attributed to the absence of protozoa, and increased propionate production and reductive acetogenesis as H 2 sinks, compared with rumen fermentation.…”

“…It is widely accepted that rumen fermentation pattern is closely related to CH 4 production due to changes in the H 2 balance such that high acetate and butyrate production enhance CH 4 production, whereas high propionate production reduces CH 4 emission (e.g. Johnson and Johnson, 1995;Moss et al, 2000). A number of studies reported both CH 4 production and rumen fermentation pattern (e.g.…”

Enteric and manure-derived methane and nitrogen emissions as well as metabolic energy losses in cows fed balanced diets based on maize, barley or grass hay

“…This is confirmed by early findings of Blaxter and Wainman (1964) testing increasing proportions of dietary maize starch in sheep. Such high-concentrate diets support the formation of propionate, which might act competitively as a hydrogen sink in the rumen compared with CH 4 (Moss et al, 2000). Still, CH 4 is also formed from non-structural carbohydrates with the amount of CH 4 depending on ruminal degradability (starch) and carbohydrate type (starch v. sugars; Hindrichsen et al, 2005;Hindrichsen and Kreuzer, 2009).…”