INTEGRATED FEEDING, MEASUREMENT AND GENOMIC APPROACHES TO MITIGATE ENTERIC METHANE EMISSIONS IN DAIRY CATTLE AND SHEEP

This thesis investigated enteric methane emissions in dairy ruminants by integrating nutritional mitigation, measurement methodologies, phenotyping and genomic analysis. In dairy cattle, the Laser Methane Detector (LMD) detected a 20% methane reduction in a commercial-farm trial using a feed additive, consistently with previous literature, while also highlighting the need for standardized protocols because measurements were affected by sampling time. A second trial confirmed good short-term repeatability but also showed variation across measurement windows and experimental weeks. In Comisana dairy ewes, GreenFeed measurements indicated relatively stable daily methane production across lactation, whereas methane intensity increased as lactation progressed. Comparison between GreenFeed and LMD showed weak agreement (R²=0.002), indicating that the two methods cannot be considered interchangeable. Finally, a GWAS conducted on 150 ewes identified 16 significant SNPs and several candidate genes related to growth, feed intake, energy and lipid metabolism. Overall, the results highlight the importance of integrating nutritional mitigation, robust measurement protocols and genetic information to improve the environmental efficiency of dairy production systems.