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Moreover, these additives are partly toxic or prohibited in animal feeding and are likely to be unavailable or too costly for (smallholder) farmers, particularly in rural regions of the world. Methane production during enteric fermentation is essential to reduce hydrogen load in the rumen and thereby maintain its functioning. Above-mentioned rumen modifiers therefore may interfere with feed digestion and thus hamper animal health and performance (Knapp et al., 2014). Hence, any strategies to increase feed use efficiency (i.e. product yield per unit of feed intake) in ruminant production, such as tactical supplementation of high-quality feeds or the processing of forages to improve their digestibility, are considered the most effective and promising mitigation measures to reduce methane emission intensity.

Optimising N-use efficiency

In terms of N (nitrogen) emissions, efficiency of N use by ruminants is very low. Even in high-yielding dairy cows, only about 25 per cent of the ingested N is converted into milk protein.