Mitigation strategies and sustainability in ruminant nutrition: in vitro studies on the reduction of methane emission by different feed additives

Methane (CH₄) emissions from ruminants are a key concern for improving the environmental sus-tainability of livestock production. This thesis investigates different strategies to reduce CH₄ emissions and enhance sustainability across five studies. The first study evaluated circular feed ingredients such as bakery by-products and wheat distiller grains in dairy cow diets. Results showed a 4.7% increase in milk yield and 22.5% reduction in milk urea nitrogen, without compromising fiber digestibility or rumen health, supporting their sustainable use. In the second study, we used the Gas Endeavour System® to standardize in vitro CH₄ measure-ments. Rumen fluid was tested from cows at different stages and feeding times. Post-feeding ru-men fluid from lactating cows produced the highest CH₄ emissions, averaging 42.3 ml/g DM compared to 33.9 ml/g DM for fasting cows. These findings highlight the importance of standard-ized protocols to ensure reliable emission data. The third study evaluated the effects of chestnut tannins and oregano essential oil on CH₄ emis-sions and rumen fermentation. Tannins reduced CH4 by 10.1% but decreased dry matter digestibil-ity by 11.9%. Oregano oil showed no significant effects under the tested conditions. The fourth study examined nitrate supplementation as a CH₄ mitigation strategy. The highest ni-trate dose (1000 mg/L) resulted in a 53.7% reduction in CH₄ emissions but also led to altered fer-mentation and a 21.4% decrease in digestibility, highlighting the need for a balanced approach to its use. The fifth study applied life cycle assessment (LCA) to evaluate the introduction of an automatic milking system (AMS) at the University of Bologna’s dairy farm. The AMS led to a 15% increase in milk yield and a 7.9% reduction in milk’s carbon footprint, demonstrating how technology can support sustainability. Overall, the thesis presents integrated strategies to mitigate CH₄ while improving productivity and resource efficiency in livestock systems.