The “Profiling Milk From Grass study” carried out in Teagasc Moorepark, investigated the effects of pasture versus indoor TMR feeding systems on a variety of milk production, composition and quality attributes. Including, the chemical composition, quality characteristics and sensory properties of raw milk, sweet cream butter and full fat cheddar cheese along with the raw milk and rumen metabolome. The experiment had 3 treatments. Group 1 was housed indoors and fed a TMR diet of grass silage, maize silage and concentrates, Group 2 was maintained outdoors on perennial ryegrass (Lolium perenne L.) only pasture (GRS), while Group 3 was also maintained outdoors on perennial ryegrass/white clover (Trifolium repens L.) pasture (CLV). Feeding system was demonstrated to have a significant effect on the composition and quality of milk and subsequent products. Milk from pasture-based systems had greater fat and protein contents, and improved protein quality compared with milk from TMR. Feeding system was demonstrated to have a significant effect on the vitamin profile of milks. Pasture feeding had a beneficial impact on the fatty acid profile of milk and dairy products with increased concentrations of beneficial nutrients such as n-3 (omega-3) fatty acids, conjugated linoleic acid, vaccenic acid and reduced levels of palmitic acid, n-6 fatty acids and thrombogenecity index score than TMR. Alterations to the fatty acid content resulted in significant rheological differences of butter and Cheddar cheeses including textural properties and color. Pasture derived products were shown to have significantly greater contents of β-carotene, imparting a yellow color on products characteristic of Irish dairy products. Sensory analysis revealed a preference for dairy products derived from the pasture-based systems compared with the TMR-based system. The application of ¹H-NMR to raw milks identified significant diet induced alterations to the milk metabolome and identified a variety of potential biomarkers of pasture derived milks. Furthermore, fatty acid profiling and ¹H-NMR metabolomics coupled with multivariate analysis demonstrated being capable of distinguishing both rumen-fluid and milk derived from cows on different feeding systems, specifically between indoor TMR and pasture-based diets used in this study.