Rethinking sustainability in modern dairy cows systems A multi-scale assessment of enteric methane emissions

This thesis investigates enteric methane production in dairy cows by examining how emissions vary and which factors influence them. The first part reviews the sustainability indicators used in European dairy farms, showing considerable differences in how these assessments are performed and a clear predominance of environmental criteria. This highlights the need for more balanced and integrated evaluation systems. The second section focuses on the difference between high and low methane emitting Italian Simmental cows. A third study analyses how lactation stage and feeding behaviour influence emissions. Shifts in metabolic demands and variation in feeding and rumination times help explain individual differences in methane output. The fourth part looks at early-life development and explores whether Saccharomyces cerevisiae supplementation can influence growth or later fermentation efficiency. Effects were limited in this study but point to the importance of early microbial establishment. The final section presents a controlled nutritional trial carried out with Aarhus University. Two additives, 3-NOP and Nitrate, showed a clear ability to reduce methane, although responses varied depending on diet and individual animal characteristics. Overall, the thesis offers a concise, multi-level view of methane emissions by linking sustainability assessment and animal management, and provides indications useful for improving the environmental performance of dairy farms.