Rumen protozoa and methanogenesis: not a simple cause–effect relationship

Abstract

Understanding the interactions between hydrogen producers and consumers in the rumen ecosystem is important for ruminant production and methane mitigation. The present study explored the relationships between rumen protozoa, methanogens and fermentation characteristics. A total of six donor sheep harbouring (F, faunated) or not (D, defaunated) protozoa in their rumens (D animals were kept without protozoa for a period of a few months (D2) or for more than 2 years (Dþ)) were used in in vitro and in vivo experiments. In vitro the absence of protozoa decreased NH 3 and butyrate production and had no effect on methane. In contrast, the liquid-associated bacterial and methanogens fraction of Dþ inocula produced more methane than D2 and F inoculum (P,0·05). In vivo fermentation parameters of donor animals showed the same trend on NH 3 and butyrate and showed that Dþ animals were high methane emitters, while D2 were the lowest (235 %). The concentration of dissolved dihydrogen measured after feeding followed the opposite trend. Methane emissions did not correlate with the relative abundance of methanogens in the rumen measured by quantitative PCR, but there was a trend for higher methanogens concentration in the solid-associated population of Dþ animals compared with D2 animals. In contrast, PCR-denaturing gradient gel electrophoresis profiles of methanogens' methyl coenzyme-M reductase A gene showed a clear clustering in liquid-associated fractions for all three groups of donors but fewer differences in solid-associated fractions. These results show that the absence of protozoa may affect differently the methanogen community and methane emissions in wethers.

Invited review: Large-scale indirect measurements for enteric methane emissions in dairy cattle: A review of proxies and their potential for use in management and breeding decisions

“…The relationship between rumen methanogen abundance and methanogenesis is less clear when changes in enteric CH 4 emissions are modulated by diet or are a consequence of selecting phenotypes related to feed efficiency or MeY. Whereas in some reports, significant positive relationships were identified (Aguinaga Casañas et al, 2015;Arndt et al, 2015;Sun et al, 2015;Wallace et al, 2015), in many others, the concentration of methanogens was unrelated to methanogenesis (e.g., Morgavi et al, 2012;Kittelmann et al, 2014;Shi et al, 2014;Bouchard et al, 2015). Bouchard et al (2015) even reported a reduction in methanogens without a significant decrease in MeP for steers fed sainfoin silage.…”

Rumen microbial (meta)genomics and its application to ruminant production

“…In addition, the genome sequence of the common rumen methanogen, Methanobrevibacter ruminantium, is available (Leahy et al, 2010) and sequencing of the genomes of other rumen methanogens is under way (see 'Rumen methanogen genome sequencing projects subsection'). However, in spite of all this information, methanogenesis in the rumen cannot be correlated to the number of methanogens (Yanez-Ruiz et al, 2008;Mosoni et al, 2011;Popova et al, 2011) or unequivocally assigned to a particular community structure Morgavi et al, 2012). Methane production is intimately associated with the concentration of hydrogen and the interactions of methanogens with other microbes producing and consuming hydrogen in the rumen (Janssen, 2010;Morgavi et al, 2010).…”

Plant components with specific activities against rumen methanogens

“…Some in vitro and in vivo studies demonstrated that the lack of the protozoal population in the rumen ecosystem has a significant effect on both the population of methanogens and the level of methane production (Cieslak et al, 2009a;Morgavi et al, 2012). The research also showed that sheep maintained without protozoa for more than 2 years have reduced methanogenesis in comparison with sheep kept without protozoa for only 2 months .…”