Effect size and land-requirements of plant-based feeding interventions to reduce methane emissions from cattle and sheep in European subalpine regions

Summary

In the past decades, hundreds of scientific studies have aimed at identifying feeding interventions to reduce the production of enteric methane (CH4) from ruminant livestock. However, mitigation measures for extensive grassland-based ruminant production systems are largely lacking, or are hardly transferred into practice. The aim of this study was to determine the effect size of plant-based feeding interventions in cattle and sheep, and to assess the feasibility of implementation by calculating the agricultural area required to grow these products. A literature research was carried out to identify plant-based feeding interventions, where the effect size was determined by at least three publications measuring CH4 in vivo in cattle or sheep, and which could be grown in temperate Europe. Using Switzerland as an example for a country with low availability of arable land and representative for grass-based ruminant production systems, it was estimated how much agricultural land would be required to grow these plant products in sufficient quantities to achieve the effects in the entire population of Swiss cattle or sheep. The review revealed that the evident effect size of plant-based feeding interventions in cattle reached only in few cases an average reduction in CH4 per unit dry matter intake (DMI) of 20%, and often stayed below 10%. For sheep, one intervention (Lotus ssp.) exceeded 30% reduction of methanogenesis, the others fitted into the results for cattle. The calculations revealed that for many products, the area required to supply them to the entire Swiss cattle population would exceed the current national area of arable land. For the effective plant-based products identified for sheep, much less agricultural land would be required, due to the small population size. Given the low efficacy of the interventions and the vast requirements for land resources to produce the respective plants, the cost of implementing them appears to exceed the benefit in greenhouse gas reduction. While feeding products of arable cultures appear hardly feasible for CH4 mitigation, implementing effective pasture plants in existing grasslands may be more practicable. Despite their comparably low efficacy to reduce CH4, including plants rich in plant secondary metabolites into multispecies swards would be a feasible approach with comparatively low risks and further benefits. Overall, the calculations reveal that the implementation of plant-based CH4 mitigators may largely increase the competition for the use of agricultural land, which is the opposite of intentions with grassland-based dairy and meat production, and which affects climate change as well.