Perspectives on the effectiveness of applicable nutritional strategies to mitigate enteric methane over different intensive dairy production system characteristics

A critical evaluation of the applicability of enteric methane mitigation strategies in relation to consistency in effect across types of dairy production systems is warranted before commercial implementation. The aim of this study is therefore to evaluate the effectiveness of selected nutritional enteric methane mitigation strategies in lowering methane emission per kg of energy-corrected (ECM), fat-corrected or fat and protein-corrected milk yield at cow level when considering animal or commercial intensive dairy system characteristics. Hence, the scope is to go beyond a traditional review of mitigation strategies providing perspectives for implementation and identification of gaps in the state-of-the-art knowledge. The evaluated strategies are increased concentrate proportion in the ration, dietary supplementation of linseed or rapeseed as lipid sources, and the dietary additives nitrate and 3-nitrooxypropanol (3-NOP). These strategies are chosen based on a high readiness for implementation and a considerable mitigation potential. A state-of-the-art is given regarding the mode of action, methane reduction potential and persistency, effect on dry matter intake and milk yield, and effects of combinations of mitigation strategies and dietary characteristics. Although scientific evidence is sometimes lacking, variation in the effectiveness of lowering enteric methane emission by mitigation strategies is to be expected across animal characteristics such as breed, life stage, stage of lactation, and production and feeding systems. This evaluation identified that future research should confirm the findings on the persistency over the lactation cycle and in the long-term. Also, effective combinations of mitigation strategies, effects on different breeds and life stages, and suitable mitigation strategies for grazing systems should be studied further.