Ruminal Methane Formation Research Articles

Rumen Lachnospiraceae isolate NK3A20 exhibits metabolic flexibility in response to substrate and coculture with a methanogen.

Hydrogen (H2) is the primary electron donor for methane formation in ruminants, but the H2-producing organisms involved are largely uncharacterized. This work integrated studies of microbial physiology and genomics to characterize rumen bacterial isolate NK3A20 of the family Lachnospiraceae. Isolate NK3A20 was the first recognized isolate of the NK3A20 group, which is among the ten most abundant bacterial genera in 16S rRNA gene surveys of rumen microbiota. NK3A20 produced acetate, butyrate, H2, and formate from glucose. The end product ratios varied when grown with different substrates and at different H2 partial pressures. NK3A20 produced butyrate as a major product using glucose or under high H2 partial pressures and switched to mainly acetate in the presence of galacturonic acid (an oxidized sugar) or in coculture with a methanogen. Growth with galacturonic acid was faster at elevated H2 concentrations, while elevated H2 slowed growth with glucose. Genome analyses revealed the presence of multiple hydrogenases including a membrane-bound Ech hydrogenase, an electron bifurcating butyryl-CoA dehydrogenase (Bcd-Etf), and an Rnf complex that may be involved in modulating the observed metabolic pathway changes, providing insight into H2 formation in the rumen. IMPORTANCE The genus-level NK3A20 group is one of the ten most abundant genera of rumen bacteria. Like most of the rumen bacteria that produce the hydrogen that is converted to methane in the rumen, it is understudied, without any previously characterized isolates. We investigated isolate NK3A20, a cultured member of this genus, and showed that it modulates hydrogen production in response to its growth substrates and the hydrogen concentration in its environment. Low-hydrogen concentrations stimulated hydrogen formation, while high concentrations inhibited its formation and shifted the fermentation to more reduced organic acid products. We found that growth on uronic acids, components of certain plant polymers, resulted in low hydrogen yields compared to glucose, which could aid in the selection of low-methane feeds. A better understanding of the major genera that produce hydrogen in the rumen is part of developing strategies to mitigate biogenic methane emitted by livestock agriculture.

3-NOP: ADME studies in rats and ruminating animals

3-NOP (3-nitrooxypropanol) reduces enteric methane formation in ruminants. A series of ADME studies in rats, lactating goats and beef cattle was performed. 3-NOP was entirely absorbed from the GIT of rats: approximately 75% of the administered 3-NOP was eliminated as carbon dioxide via exhalation and approximately 20% were excreted via urine. 3-NOP is oxidized to 3-nitrooxypropionic acid (NOPA) which is then hydrolyzed to 3-hydroxypropionic acid (HPA) and inorganic nitrate, the major rat plasma metabolites. NOPA is also a plasma metabolite in beef. The metabolism of 3-NOP is fast as indicated by the negligible amounts of 3-NOP found in rat plasma 2 h after dosing. HPA is a naturally occurring metabolite. It is either metabolized into carbon dioxide and acetyl-CoA or into propanoyl-CoA, the latter serves as substrate for gluconeogenesis. Gluconeogenesis is very prominent in lactating ruminants which use propanoyl-CoA as their main carbon source. Thus, the formation of lactose from 3-NOP by lactating goats is not unexpected. Lactose was the major metabolite of 3-NOP in the aqueous phase of milk. The incorporation of 3-NOP into endogenous metabolism makes it difficult to derive a marker residue, however, conservative risk assessment could be based on the measured radioactivity in tissues.

Meta‐analysis of the relationship between dietary tannin level and methane formation in ruminants from in vivo and in vitro experiments

A meta-analysis was conducted to evaluate the extent to which dietary tannin level is related to methane emissions from ruminants. Data from a total of 30 experiments comprising 171 treatments were entered in a database. In vitro batch culture and in vivo measurements were distinguished as experimental approaches. With any approach, methane declined when dietary tannins increased. The in vitro approach predicted the in vivo response quite accurately. However, in vitro, the response followed a quadratic response pattern (R(2) = 0.66; lower response with increasing tannin level), whereas in vivo, this decline was linear (R(2) = 0.29). This indicates that the in vitro batch culture is of limited accuracy for estimating effects at levels >100 g tannin/kg dry matter. The large variation in methane/digestible organic matter (OM) found at low tannin levels may explain contrasting literature reports. Methane reduction with tannins was associated with a reduced apparent digestion of OM, and especially fibre, but methane/apparently digestible OM declined also. The present findings are helpful as they identified an underlying general antimethanogenic effect of tannins across tannin sources and experimental conditions, thus allowing concentrating the search on sources with satisfactory palatability and low adverse effects on animal performance.

Characterization of rumen ciliate community composition in domestic sheep, deer, and cattle, feeding on varying diets, by means of PCR-DGGE and clone libraries

The structure and variability of ciliate protozoal communities in the rumens of domestic New Zealand ruminants feeding on different diets was investigated. The relative abundance of ciliates compared with bacteria was similar across all samples. However, molecular fingerprinting of communities showed ruminant-specific differences in species composition. Community compositions of cattle were significantly influenced by diet. In contrast, diet effects in deer and sheep were weaker than the animal-to-animal variation. Cloning and sequencing of almost-full-length 18S rRNA genes from representative samples revealed that New Zealand ruminants were colonized by at least nine genera of ciliates and allowed the assignment of samples to two distinct community types. Cattle contained A-type communities, with most sequences closely related to those of the genera Polyplastron and Ostracodinium. Deer and sheep (with one exception) harboured B-type communities, with the majority of sequences belonging to the genera Epidinium and Eudiplodinium. It has been suggested that species composition of ciliate communities may impact methane formation in ruminants, with the B-type producing more methane. Therefore, manipulation of ciliate communities may be a means of mitigating methane emissions from grazing sheep and deer in New Zealand.

Diet composition affects the level of ruminal methane suppression by medium-chain fatty acids

In 3 experiments, the methane-suppressing effects of medium-chain fatty acids were investigated using basal diets of extensive type (high structural carbohydrate content) and intensive type (low structural carbohydrate content). In Expt 1, sheep were fed the extensive-type diet supplemented with 60 g/kg of rumen-protected fat (control) or coconut oil. The use of coconut oil in the diet did not clearly reduce methane release from the total digestive tract. In 2 in vitro experiments carried out with a RUSITEC apparatus, interactions of either coconut oil (Expt 2) or pure non-esterified lauric acid (Expt 3) with the 2 types of basal diet were determined using 2 × 2 factorial designs. Expt 2 confirmed a high efficacy of coconut oil against methane release in the intensive-type diet (suppression by 62% relative to control) and a reduced efficiency in the extensive-type diet (suppression by 6% relative to control). In contrast, pure lauric acid supplementation suppressed methane release in vitro by approximately 80%, and this was independent of the basal-diet type used. The results suggest that interactions of fat with the basal diet in the rumen have to be taken into consideration to develop effective feeding strategies against ruminal methane formation.