Metabolic versatility enables acetogens to colonize ruminants with diet-driven niche partitioning.

Enteric methane emissions are energy losses from farmed ruminants and contribute to global warming. Diverting electrons and H2 flow toward beneficial fermentation products would mitigate ruminal methane emissions while improving feed efficiency. Acetogens can direct H2 and electrons to acetate production via the Wood-Ljungdahl pathway, but methanogens have more competitive H2 affinities.

Interaction Between Ruminal Acetate Infusion and Diet Fermentability on Milk Fat Production in Dairy Cows.

Acetate is naturally produced in the rumen through feed degradation and fermentation. It serves as a primary energy source for ruminants and as a key substrate for de novo fatty acid synthesis in the mammary gland. The interaction of exogenous acetate with different animal and dietary factors is an area of growing interest, as it may have significant implications for milk fat synthesis.

Volatile Cues from Fresh Cattle Dung Can Drive Horn Fly Egg-Laying and Fecal Attraction to Horn Flies, (Diptera: Muscidae).

The horn fly is an economically important hematophagous ectoparasite of cattle. Its management relies heavily on broad-spectrum pesticides, which are harmful to the environment and have led to the development of resistance. Therefore, alternative control methods are needed.

Reductive acetogenesis is a dominant process in the ruminant hindgut.

Background: The microbes residing in ruminant gastrointestinal tracts play a crucial role in converting plant biomass to volatile fatty acids, which serve as the primary energy source for ruminants. This gastrointestinal tract comprises a foregut (rumen) and hindgut (cecum and colon), which differ in structures and functions, particularly with respect to feed digestion and fermentation. While the rumen microbiome has been extensively studied, the cecal microbiome remains much less investigated and understood, especially concerning the assembling microbial communities and overriding pathways of hydrogen metabolism.

Feed additives for methane mitigation: A guideline to uncover the mode of action of antimethanogenic feed additives for ruminants.

This publication aims to provide guidelines of the knowledge required and the potential research to be conducted in order to understand the mode of action of antimethanogenic feed additives (AMFA). In the first part of the paper, we classify AMFA into 4 categories according to their mode of action: (1) lowering dihydrogen (H) production; (2) inhibiting methanogens; (3) promoting alternative H-incorporating pathways; and (4) oxidizing methane (CH). The second part of the paper presents questions that guide the research to identify the mode of action of an AMFA on the rumen CH production from 5 different perspectives: (1) microbiology; (2) cell and molecular biochemistry; (3) microbial ecology; (4) animal metabolism; and (5) cross-cutting aspects.

Feed additives for methane mitigation: Recommendations for testing enteric methane-mitigating feed additives in ruminant studies.

There is a need for rigorous and scientifically-based testing standards for existing and new enteric methane mitigation technologies, including antimethanogenic feed additives (AMFA). The current review provides guidelines for conducting and analyzing data from experiments with ruminants intended to test the antimethanogenic and production effects of feed additives. Recommendations include study design and statistical analysis of the data, dietary effects, associative effect of AMFA with other mitigation strategies, appropriate methods for measuring methane emissions, production and physiological responses to AMFA, and their effects on animal health and product quality.

Feed additives for methane mitigation: Recommendations for identification and selection of bioactive compounds to develop antimethanogenic feed additives.

Despite the increasing interest in developing antimethanogenic additives to reduce enteric methane (CH) emissions and the extensive research conducted over the last decades, the global livestock industry has a very limited number of antimethanogenic feed additives (AMFA) available that can deliver substantial reduction, and they have generally not reached the market yet. This work provides technical recommendations and guidelines for conducting tests intended to screen the potential to reduce, directly or indirectly, enteric CH of compounds before they can be further assessed in in vivo conditions. The steps involved in this work cover the discovery, isolation, and identification of compounds capable of affecting CH production by rumen microbes, followed by in vitro laboratory testing of potential candidates.

Effects of type of substrate and dilution rate on fermentation in serial rumen mixed cultures.

Forages and concentrates have consistently distinct patterns of fermentation in the rumen, with forages producing more methane (CH) per unit of digested organic matter (OM) and higher acetate to propionate ratio than concentrates. A mechanism based on the Monod function of microbial growth has been proposed to explain the distinct fermentation pattern of forages and concentrates, where greater dilution rates and lower pH associated with concentrate feeding increase dihydrogen (H) concentration through increasing methanogens growth rate and decreasing methanogens theoretically maximal growth rate, respectively. Increased H concentration would in turn inhibit H production, decreasing methanogenesis, inhibit H-producing pathways such as acetate production via pyruvate oxidative decarboxylation, and stimulate H-incorporating pathways such as propionate production.

Invited review: Current enteric methane mitigation options.

Ruminant livestock are an important source of anthropogenic methane (CH). Decreasing the emissions of enteric CH from ruminant production is strategic to limit the global temperature increase to 1.5°C by 2050.

Dietary selection of metabolically distinct microorganisms drives hydrogen metabolism in ruminants.

Ruminants are important for global food security but emit the greenhouse gas methane. Rumen microorganisms break down complex carbohydrates to produce volatile fatty acids and molecular hydrogen. This hydrogen is mainly converted into methane by archaea, but can also be used by hydrogenotrophic acetogenic and respiratory bacteria to produce useful metabolites.

3-Nitrooxypropanol substantially decreased enteric methane emissions of dairy cows fed true protein- or urea-containing diets.

Methane is a potent but short-lived greenhouse gas targeted for short-term amelioration of climate change, with enteric methane emitted by ruminants being the most important anthropogenic source of methane. Ruminant production also releases nitrogen to the environment, resulting in groundwater pollution and emissions of greenhouse gas nitrous oxide. We hypothesized that inhibiting rumen methanogenesis in dairy cows with chemical inhibitor 3-nitrooxypropanol (3-NOP) would redirect metabolic hydrogen towards synthesis of microbial amino acids.

Long-Term and Carryover Effects of Supplementation with Whole Oilseeds on Methane Emission, Milk Production and Milk Fatty Acid Profile of Grazing Dairy Cows.

Research is ongoing to find nutritional methane (CH) mitigation strategies with persistent effects that can be applied to grazing ruminants. Lipid addition to dairy cow diets has shown potential as means to decrease CH emissions. This study evaluated the effects of oilseeds on CH emission and production performance of grazing lactating dairy cows.

Effect of Oats and Wheat Genotype on In Vitro Gas Production Kinetics of Straw.

Increases in cereals grain yield in the last decades have increased the accumulation of straw on the soil after harvest. Farmers typically open burn the straw to prepare the soil for the next crop, resulting in pollution, emission of greenhouse gases, erosion, loss of soil organic matter, and wildfires. An alternative is feeding straw to ruminants, but straw nutritive value is limited by its high content of lignocellulose and low content of protein.

Association of fibre degradation with ruminal dissolved hydrogen in growing beef bulls fed with two types of forages.

The present study investigated the association between fibre degradation and the concentration of dissolved molecular hydrogen (H2) in the rumen. Napier grass (NG) silage and corn stover (CS) silage were compared as forages with contrasting structures and degradation patterns. In the first experiment, CS silage had greater 48-h DM, neutral-detergent fibre (NDF) and acid-detergent fibre degradation, and total gas and methane (CH4) volumes, and lower 48-h H2 volume than NG silage in 48-h in vitro incubations.

Inhibiting Methanogenesis Stimulated de novo Synthesis of Microbial Amino Acids in Mixed Rumen Batch Cultures Growing on Starch but Not on Cellulose.

Ameliorating methane (CH) emissions from ruminants would have environmental benefits, but it is necessary to redirect metabolic hydrogen ([H]) toward useful sinks to also benefit animal productivity. We hypothesized that inhibiting rumen methanogenesis would increase de novo synthesis of microbial amino acids (AA) as an alternative [H] sink if sufficient energy and carbon are provided. We examined the effects of inhibiting methanogenesis with 9, 10-anthraquione (AQ) on mixed rumen batch cultures growing on cellulose or starch as sources of energy and carbon contrasting in fermentability, with ammonium (NH) or trypticase (Try) as nitrogen (N) sources.

Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions.

Rumen fermentation affects ruminants productivity and the environmental impact of ruminant production. The release to the atmosphere of methane produced in the rumen is a loss of energy and a cause of climate change, and the profile of volatile fatty acids produced in the rumen affects the post-absorptive metabolism of the host animal. Rumen fermentation is shaped by intracellular and intercellular flows of metabolic hydrogen centered on the production, interspecies transfer, and incorporation of dihydrogen into competing pathways.

Inhibiting Methanogenesis in Rumen Batch Cultures Did Not Increase the Recovery of Metabolic Hydrogen in Microbial Amino Acids.

There is an interest in controlling rumen methanogenesis as an opportunity to both decrease the emissions of greenhouse gases and improve the energy efficiency of rumen fermentation. However, the effects of inhibiting rumen methanogenesis on fermentation are incompletely understood even in in vitro rumen cultures, as the recovery of metabolic hydrogen ([H]) in the main fermentation products consistently decreases with methanogenesis inhibition, evidencing the existence of unaccounted [H] sinks. We hypothesized that inhibiting methanogenesis in rumen batch cultures would redirect [H] towards microbial amino acids (AA) biosynthesis as an alternative [H] sink to methane (CH).

Nitrate improves ammonia incorporation into rumen microbial protein in lactating dairy cows fed a low-protein diet.

Generation of ammonia from nitrate reduction is slower compared with urea hydrolysis and may be more efficiently incorporated into ruminal microbial protein. We hypothesized that nitrate supplementation could increase ammonia incorporation into microbial protein in the rumen compared with urea supplementation of a low-protein diet fed to lactating dairy cows. Eight multiparous Chinese Holstein dairy cows were used in a crossover design to investigate the effect of nitrate or an isonitrogenous urea inclusion in the basal low-protein diet on rumen fermentation, milk yield, and ruminal microbial community in dairy cows fed a low-protein diet in comparison with an isonitrogenous urea control.

Inhibition of Rumen Methanogenesis and Ruminant Productivity: A Meta-Analysis.

Methane (CH) formed in the rumen and released to the atmosphere constitutes an energy inefficiency to ruminant production. Redirecting energy in CH to fermentation products with a nutritional value to the host animal could increase ruminant productivity and stimulate the adoption of CH-suppressing strategies. The hypothesis of this research was that inhibiting CH formation in the rumen is associated with greater ruminant productivity.

Molecular hydrogen generated by elemental magnesium supplementation alters rumen fermentation and microbiota in goats.

We tested the hypotheses that supplementation of a diet with elemental Mg increases ruminal dissolved H2 (dH2) in rumen fluid, which in turn alters rumen fermentation and microbial community in goats. In a randomised block design, twenty growing goats were allocated to two treatments fed the same basal diet with 1·45 % Mg(OH)2 or 0·6 % elemental Mg. After 28 d of adaptation, we collected total faeces to measure total tract digestibility, rumen contents to analyse fermentation end products and microbial groups, and measured methane (CH4) emission using respiration chambers.