Methane Mitigation Strategies
Methane reduction strategies either function directly upon the methane generating bacteria , or by limiting the substrate availability for methanogenesis.  It is predominantly the carbohydrate content of the diet which influences rumen pH, and this in turn determines the ruminal biome. Dietary factors such as dry matter intake, lignin and neutral detergent fibre components,along with cellulose and hemicellulose, all increase methane production, (Holter and Young, 1992). In contrast,methane production is reduced when the ruminal pH is low and the transit time of ingesta is decreased. 

It must be remembered that the rumen is a biological system and so the balance of rapidly fermentable carbohydrates within a ration must remain within the functional capacity of the ruminal microbiome. Once volatile fatty acid production outstrips absorption, subacute ruminal acidosis is at risk of developing and rumen functionality is reduced. Taking a global perspective, it is imperative to note that the reduction in methane production created by feeding highly digestible carbohydrates eg. maize, may be far outstripped by the GHG emissions of carbon dioxide released by land use change from grassland, forest or wetland into cultivatable land.

Both fatty acids eg. myristic acid, and oils (lipids) have the ability to inhibit the methane production.  The former increase propionic acid production, while the latter, by removing the hydrogen required for methane production, by the biohydrogenation of unsaturated fatty acids, directly reduce methane output . Due to the proven synergy of combinations of fatty acids, it is apparent that oil supplementation eg. sunflower and linseed oil, will provide a greater decrease in methane than the use of individual fatty acids. Linseed oil fed at 5% of Dry Matter to dairy cows has shown a 50% reduction in daily methane output. 

Plant compounds, including tannins, saponins and essential oils can also reduce methane production by acting as hydrogen acceptors within the rumen. The complexities of dietary manipulations are evident, with for example, the addition of tannins not always proving effective in reducing methane output. The addition of lipids can affect the ration’s palatability and dry matter intake, as well as altering milk components, so future research is required to maximise the efficacy long term of these supplements.  

Modification of the ruminant diet does not represent the panacea for the future sustainability of livestock farming. Instead, it is a tactic within the play book, which will help achieve the twin aims of feeding the world whilst minimising the deleterious environmental effects. The reported 1.3 billion tons of food wastage annually clearly indicates that food security is as much a food distribution issue, as it is a food production problem. As emerging economies continue to develop, the population of 1 billion who already consume calorie dense, nutrient poor diets will be expected to rise. To ensure a palatable food future, the ability of the consumer to make balanced dietary choices must combine with sustainable farming practices, incorporating some of the ruminant nutritional practices described above, and an increased efficiency of food production from farm to fork.


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