Abstract
Methane (CH4) is produced as an end product from feed fermentation in the rumen. Yield of CH4 varies between individuals despite identical feeding conditions. To get a better understanding of factors behind the individual variation, 73 dairy cows given the same feed but differing in CH4 emissions were investigated with focus on fiber digestion, fermentation end products and bacterial and archaeal composition. In total 21 cows (12 Holstein, 9 Swedish Red) identified as persistent low, medium or high CH4 emitters over a 3 month period were furthermore chosen for analysis of microbial community structure in rumen fluid. This was assessed by sequencing the V4 region of 16S rRNA gene and by quantitative qPCR of targeted Methanobrevibacter groups. The results showed a positive correlation between low CH4 emitters and higher abundance of Methanobrevibacter ruminantium clade. Principal coordinate analysis (PCoA) on operational taxonomic unit (OTU) level of bacteria showed two distinct clusters (P < 0.01) that were related to CH4 production. One cluster was associated with low CH4 production (referred to as cluster L) whereas the other cluster was associated with high CH4 production (cluster H) and the medium emitters occurred in both clusters. The differences between clusters were primarily linked to differential abundances of certain OTUs belonging to Prevotella. Moreover, several OTUs belonging to the family Succinivibrionaceae were dominant in samples belonging to cluster L. Fermentation pattern of volatile fatty acids showed that proportion of propionate was higher in cluster L, while proportion of butyrate was higher in cluster H. No difference was found in milk production or organic matter digestibility between cows. Cows in cluster L had lower CH4/kg energy corrected milk (ECM) compared to cows in cluster H, 8.3 compared to 9.7 g CH4/kg ECM, showing that low CH4 cows utilized the feed more efficient for milk production which might indicate a more efficient microbial population or host genetic differences that is reflected in bacterial and archaeal (or methanogens) populations.
Highlights
Ruminants are unique in their ability to utilize feeds rich in cellulose, most likely due to the great diversity of microorganisms that break down feed in the rumen of the host animal
For the 73 dairy cows included in the study, average daily dry matter intake was 23.7 ± 2.7 kg/day and energy corrected milk (ECM) yield was 34.6 ± 6.2 kg/day [least square mean ± standard error (s.e.)] (Supplementary Table 1)
The main difference in the present study was found at species level, where the relative abundance of M. gottschalkii clade was linked with higher CH4 production, and relative abundance of M. ruminantium was related to low CH4 production
Summary
Ruminants are unique in their ability to utilize feeds rich in cellulose, most likely due to the great diversity of microorganisms that break down feed in the rumen of the host animal. Various mitigation strategies have been evaluated with the aim of reducing CH4 emissions, including for example using different feed and feedstuffs high in lipids, ionophores, plant compounds such as tannins and enzymes (Beauchemin et al, 2009; Hook et al, 2010; Cieslak et al, 2013). These strategies have produced varying results, but with no significant longterm effect. The use of 3-nitrooxypropanol, a compound designed to inhibit the activity of the enzyme responsible for formation of CH4 (Duval and Kindermann, 2012), was shown to reduce CH4 emissions in dairy cows without any signs of toxic effects on the animal and no or a minor effect on DMI (Reynolds et al, 2014; Hristov et al, 2015; Lopes et al, 2016)
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