Grass-based milk production is a major contributor to Irish agricultural output, and the terms "grass-fed" and "pasture-raised" are appreciated by many consumers as a more sustainable and welfare friendly means of producing milk. This study characterised the Irish raw milk pool using SIRA of carbon, nitrogen, oxygen and sulphur. Authentic raw milk samples were collected from 50 farms on five occasions over 13 months. δ13C values reflected a high level of grass input, and values increased with increasing cereal concentrate feed input (P < 0.001). δ18O values were most negative in spring. There was a significant interaction between feed and season for δ13C and δ15N values (P < 0.05), with the impact of concentrate feeding most evident in spring. The isotopic ratio values of the Irish milk pool may serve as authenticity markers with the potential to discriminate Irish milk and dairy products from similar commodities from other countries.
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