## 1 Introduction  
Milk and dairy products are highly nutritious food stuffs for individuals throughout all stages of life. The composition of milk directly influences the quality, yield, functionality, and nutritional value of milk and dairy products. A number of factors affect the composition of milk namely, breed, stage of lactation, health status of the cow, and diet. Dietary factors, in particular, affect the composition and nutritional content of milks through manipulation of the fatty acids (FA) profile, while cow breed can influence the composition of milk proteins. Therefore, selection of appropriate farm management practices offers one way of modulating milk composition and processing properties. Extensive research has been carried out examining the effects of pasture or conventional total mixed ration (TMR) on the composition and quality of milk and dairy products. Pasture-based feeding of cows, which is estimated to account for \(\sim\)10% of the global milk supply [1], has been demonstrated to have beneficial effects on the nutritional profile of milk. These include significant decreases in the proportion of saturated fatty acids (SFA), particularly C16:0, and omega 6 FAs, and increased amounts of polyunsaturated fatty acids (PUFA), along with nutritionally beneficial FAs such as conjugated linoleic acid, branched chain, and omega 3 FA [2; 3]. Indeed, [PERSON] et al. [4] demonstrated a linear response for many of these nutrients with increasing proportion of pasture in the cow diet. Pasture-feeding induced alterations to the FA profile of milk and also had a significant effect on the volatile and sensory properties of milk [5], and composition and quality of products such as sweet cream butter [6] and full-fat checkdar cheese [7]. [PERSON] et al. [8] demonstrated a significant effect between warm season pasture feed versus TMR feed on milk fatty acid profile, but also highlighted that cow breed can have an influence on the fatty acid profile of milks. Several factors determine the suitability of dairy feeding systems to particular regions of the world namely, climate, environmental conditions, soil properties, availability of grazing lands, and dietary requirements of the animals. Ireland has a predominantly temperate climate with plentiful rainfall providing ideal conditions for the growth of pastures and with that a seasonal pasture-based dairy system. As such, [PERSON] et al. [9] demonstrated that forage, particularly grazed pasture, was the largest component (76%) of the Irish cows annual diet as measured over a three-year period. There are a wide variety of benefits associated with the use of pasture-based feeding systems, including improved consumer perceptions of pasture derived products as being a healthy and animal friendly, improved environmental sustainability, and a cheap source of highly nutritious feed for the cow compared to conventional TMR practises. There are, however, also certain limitations to the use of pasture-based feeding systems, which can include, but are not limited to, a seasonal rather than annual supply of milk to producers, \"peak\" milk production periods, seasonal based changes in milk composition, and limitations of grass growth during certain periods of the year. Given this dependence of pasture availability on climate and environment, there are periods of the year, and potential for non-typical weather occurrences such as drought, when pasture-based systems will require input of concentrate supplements to meet the energy requirements of high yielding cows. Choice of supplemental feed source will inevitably affect the composition, quality, and processability of milk. Therefore, greater knowledge is required on the impact of the different supplement choices on milk quality and usability, to allow farmers and manufacturers to make more informed decisions taking into account subsequent downstream effects on product quality.