| Phillip Lancaster, MS, PhD Ruminant nutritionist Beef Cattle Institute Kansas State University palancaster@vet.k-state.edu |
Enteric methane from rumen fermentation accounts for more than 50% of the greenhouse gas emissions from beef production. Cattle consuming forage diets have approximately twice the methane yield (6.5 vs 3.0% of feed intake) compared to cattle on high-grain diets. Thus, the cow-calf and stocker sector of the beef industry account for 90% of methane emissions and 85% of total greenhouse gas emissions of beef production. However, a large portion of the methane emissions can be offset by carbon sequestration with proper grazing management.
How does the beef industry work to further reduce methane emissions from grazing cattle? In a previous article, we talked about feed additives to reduce enteric methane emissions. There has been a lot of research on different feed additives such as seaweed, nitrate, lipids, and 3NOP with a lot of interest in some of these compounds. Feed additives work by capturing hydrogen before methanogenic bacteria can convert it to methane or by inhibiting methanogenic bacteria directly and can reduce methane emissions 20 to 50% when fed to cattle daily. However, feed additives that must be fed daily are not practical in grazing cattle production systems.
One strategy that could be used to reduce methane emissions of grazing cattle is to plant certain forage species with anti-methanogenic properties. Many plant species (legumes, forbs, and herbs) produce bioactive compounds that reduce enteric methane emissions. These compounds include tannins, saponins, phenolic acids, flavonoids, xanthones, lignans, and stilbenes, which vary in concentration among forage plants.
There are 2 forms of tannins, condensed and hydrolysable, found in plants and plants differ in the amount of each form they produce. Condensed tannins reduce methane emissions but can also reduce protein digestibility, nutrient absorption, and animal productivity. However, this does not happen in every case. Hydrolysable tannins have a direct effect on methanogenic bacteria without reducing forage digestion, and thus, may be more practical. Saponins are a subclass of terpenoid compounds that inhibit rumen ciliate protozoa that produce hydrogen. Without the hydrogen available, methanogenic bacteria cannot convert carbon dioxide to methane. However, saponins can contribute to stable foam in the rumen that can cause bloat, thus the proportion of saponin-containing plants in the pasture needs to be limited. The other secondary compounds (phenolic acids, flavonoids, xanthones, lignans, and stilbenes) have demonstrated ability to reduce methane emissions but less is known about the mode of action in the rumen.
Plant species vary in the concentration of bioactive compounds they contain and thus varying degrees of methane-reducing ability. Some plant species that have been evaluated for their effect on methane production are listed in Table 1. The lotus spp. includes plants like birdsfoot trefoil and narrowleaf trefoil which are nitrogen fixing legumes and would provide other benefits to the pasture besides methane reduction. Sainfoin and sulla are other nitrogen-fixing legumes that would be beneficial in pastures and could also reduce methane emissions. All of these legumes have minimal to no bloat risk. Biserrula is an annual legume that contains phenolic compounds and saponins. Chicory and plaintain are perennial herbs with the ability to reduce methane emissions. Many of these plant species can enhance animal performance through increasing digestibility of the forage consumed and increasing protein intake in the case of legumes. However, caution should be used when establishing these forage species in pastures as grazing pastures with high (>40%) proportions of these plant species and the bioactive compounds they contain can reduce productivity of growing animals.
Grass forage plants contain minimal to no bioactive compounds with methane reducing capability. Thus, including legumes and forbs in pasture plantings is necessary to increase the consumption of bioactive compounds by grazing cattle. Plant biodiversity in pastures is not only sustainable from wildlife and soil health perspective but may also reduce the methane emissions. Many of the plants with methane-reducing ability are not commonly grown for grazing. One thing to note is that many of the studies calculating the methane emissions for the cow-calf and stocker sectors utilize data based on common forage species. Therefore, operations that include high levels of biodiversity of forage plants may have less than expected methane emissions.
| Table 1. Pasture forage species with bioactive compounds that reduce methane emissions from cattle | ||
| Plant Species | Expected Methane Reduction | Bioactive Compounds |
| Lotus spp. | -38% | Condensed tannins |
| Sanfoin | -13% | Condensed tannins, Phenolic compounds |
| Sulla | -32% | Hydrolysable tannins, Saponins |
| Biserrula | -77% | Phenolic compounds |
| Chicory | -11% | Condensed tannins, Phenolic compounds, Saponins |
| Plaintain | -18% | Condensed tannins, Saponins |
| Data adapted from Badgery et al. (2023; https://doi.org/10.1071/CP22299) | ||
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