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Study of the efficacy of methanogenesis inhibitors in the rumen has given inconsistent results, mainly due to poorly understood effects on the key microbial groups involved in pathways for methane (CH4) synthesis. The experiment described in this report was designed to assess the effect of propyl propane thiosulfinate (PTS), diallyl disulfide (DDS) and bromochloromethane (BCM) on rumen fermentation, methane production and microbial populations in continuous culture fermenters. No effects on total volatile fatty acids (VFA) were observed with PTS or DDS, but VFA were decreased with BCM. Amylase activity increased with BCM as compared with the other treatments. A decrease in methane production was observed with PTS (48%) and BCM (94%) as compared with control values. The concentration of methanogenic archaea decreased with BCM from day 4 onward and with PTS on days 4 and 8. Pyrosequencing analysis revealed that PTS and BCM decreased the relative abundance of Methanomicrobiales and increased that of Methanobrevibacter and Methanosphaera. The total concentration of bacteria was not modified by any treatment, although treatment with BCM increased the relative abundance of Prevotella and decreased that of Ruminococcus. These results suggest that the inhibition of methane production in the rumen by PTS and BCM is associated with a shift in archaeal biodiversity and changes in the bacterial community with BCM., (© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The aim of this work was to study whether feeding a methanogen inhibitor from birth of goat kids and their does has an impact on the archaeal population colonizing the rumen and to what extent the impact persists later in life. Sixteen goats giving birth to two kids were used. Eight does were treated (D+) with bromochloromethane after giving birth and over 2 months. The other 8 goats were not treated (D-). One kid per doe in both groups was treated with bromochloromethane (k+) for 3 months while the other was untreated (k-), resulting in four experimental groups: D+/k+, D+/k-, D-/k+, and D-/k-. Rumen samples were collected from kids at weaning and 1 and 4 months after (3 and 6 months after birth) and from does at the end of the treating period (2 months). Pyrosequencing analyses showed a modified archaeal community composition colonizing the rumen of kids, although such effect did not persist entirely 4 months after; however, some less abundant groups remained different in treated and control animals. The different response on the archaeal community composition observed between offspring and adult goats suggests that the competition occurring in the developing rumen to occupy different niches offer potential for intervention.

Ricinoleic acid (RA; 12-hydroxy-cis-9-18:1) is the main fatty acid component of castor oil. Although a precursor for CLA synthesis in lactic acid bacteria, RA was found previously not to form CLA in ruminal digesta but to have some inhibitory properties. The present study was undertaken to evaluate the potential of RA to modulate ruminal biohydrogenation and methanogenesis. Ruminal digesta from 4 sheep receiving a mixed hay-concentrate diet was incubated in vitro with 0.167 g/L of linoleic acid (LA; cis-9,cis-12-18:2) or with a combination of LA and RA or LA and castor oil (LA, RA, and castor oil added to a final concentration of 0.167 g/L) in the presence and absence of lipase. The CLA rumenic acid (cis-9,trans-11-18:2) accumulated when either RA or castor oil and lipase was present. Vaccenic acid (VA; trans-11-18:1) also accumulated, and a decrease of the rate of production of stearic acid (SA; 18:0) was observed. When LA was incubated with castor oil in the absence of lipase, no effects on biohydrogenation were observed. Ricinoleic acid at 0.02 g/L did not affect growth of Butyrivibrio fibrisolvens but it inhibited growth of Butyrivibrio proteoclasticus. Butyrivibrio proteoclasticus but not B. fibrisolvens metabolized RA to 12-hydroxystearate. Linoleic acid metabolism by B. proteoclasticus appeared to be unaffected by RA addition whereas rumenic acid accumulation increased (P = 0.015 at 12 h) when RA was added. A 28% decrease (P = 0.004) in methane was obtained in 24 h in vitro incubations of diluted buffered ruminal fluid with added 0.2 g RA/L. There was no effect on the total concentration of VFA after 24 h as a result of RA addition, but the molar proportions of acetate and butyrate were decreased (P = 0.041 and P < 0.001, respectively) whereas that of propionate increased (P < 0.001). It was concluded that, at least in vitro, RA or the combination of castor oil and lipase inhibit biohydrogenation, causing the accumulation of rumenic acid and VA, with potential health benefits for ruminant products. The effect appeared to be mediated via an inhibitory effect on the biohydrogenating activity of B. proteoclasticus. An added environmental benefit could be a concomitant decrease in methane emissions. In vivo studies are now required to confirm the potential of these additives.