Effect of Diet on the Stable Isotopes of Carbon and Nitrogen in Cow-Sheep-Goat Milk - Abstract Paraskevi Chantzi 1,2, Nives Ogrinc 3, Doris Potočnik 3, Stella Dokou 1, Ilias Giannenas 1, Michalis Vernikos 2 and Nektarios D. Giadinis 4 1 Laboratory of Nutrition, Faculty of Veterinary Medicine, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 2 Union of Agricultural Cooperatives of Naxos, 84300 Cyclades, Greece 3 Department of Environmental Sciences, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 4 Clinic of Farm Animals, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece Summary 1 Twelve (12) bulk samples of Holstein cow’s milk, fifteen (15) bulk samples of sheep and goat’s milk, and forty-three (43) feed samples were collected in August 2020 from livestock farms in Naxos Island, South Aegean, Greece. Three milk samples were taken from milk coolers in 25ml falcon bottles from each station and subjected to isotopic analysis to determine their carbon (13C/12C) and nitrogen (15N/14N) isotopic ratios. The isotopic values of the feed ranged from -26.1 ‰ to -16.8 ‰ for δ13C (mean value -21.4‰) and from 1.5‰ to 6.5‰ for δ15N (mean value 3.9‰). When plotted again each other (fig. 1), the samples could be discriminated into three groups. The first group corresponded mainly to cow feed with lower δ 15N values (1.3‰ to 2.8‰), while the second group is represented by cow feed with higher δ 15N values (3.5‰ to 6.5‰ and lower δ13C values (-26.1‰ to -23.9‰). The third group is made up predominantly of sheep/goat feed with higher δ 15N values (3.8‰ and 6.5‰) and δ13C values (-21.7‰ to -16.8‰). From the carbon and nitrogen values of soya [δ13C: -26.6‰, δ15N: 0.7‰] and maize [δ13C: -11.8‰, δ15N: 4.3‰] used in the sampled feed, it can be concluded that both feed components determine the isotopic record of feed rations. Milk casein isotopic values ranged from -24.4‰ to -18.1‰ for δ13C (mean value -20.7‰) and from 3.9‰ to 8.4‰ for δ15N (mean value 5.7‰). The δ13Ccasein values in cow milk were also higher than in feed for - 3.14‰ and 2.96‰ agreeing with the δ13Cfeed-casein values reported in the literature. In addition, a 1-4 ‰ increase in the δ13C ‰ values are reported during the metabolism of feed into milk protein, while feeding maize results in a -4‰ reduction. The data from this study shows that animal proteins were naturally 15N-enriched relative to their diet (δ15Νfeed-milk = -4.3 to -1.1‰), a trophic shift consistent with reported values for dairy cows (2.4‰ and 3.2‰) and in growing cattle (3.6‰ and 3.8‰). The δ13Cfeed-casein (-5.5‰ to 4.4‰) and δ15Νfeed-milk (-4.1‰ to 0.6‰) for sheep/goat samples were higher, reflecting a semi-extensive type of farming and those environmental parameters that affect the isotopic record. Proceedings of HAICTA 2022, September 22–25, 2022, Athens, Greece EMAIL: pchantzi@geo.auth.gr (A. 1); nives.ogrinc@ijs.si (A. 2); doris.potocnik@ijs.si (A. 3); dgstylian@gmail.com (A. 4); igiannenas@vet.auth.gr (A. 5); m.vernikos@easnaxos.com (A. 6); ngiadini@vet.auth.gr (A. 7) ORCID: 0000-0001-5444-4887 (A. 1); 0000-0002-5709-1594 (A. 2); 0000-0002-4636-5916 (A. 3); 0000-0002-0181-8416 (A. 4); 0000-0003- 3145-3734 (A. 5); 0000-0001-5646-3627 (A. 7) ©️ 2022 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0). CEUR Workshop Proceedings (CEUR-WS.org) 510 7 Group II 6 Group III 5 4 δ15Ν ‰ V-AIR maize 3 soya cow feed 2 sheep/goat feed Group I 1 0 -30 -25 -20 -15 -10 -5 δ C ‰ V-PDB 13 Figure 1: Carbon and nitrogen isotope values for feed samples from livestock farms in Naxos Island, South Aegean, Greece Keywords Isotopes, carbon, nitrogen, milk, feed, traceability, authenticity Acknowledgements This research was funded by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship, and Innovation, under the call RESEARCH – CREATE – INNOVATE (project code: Τ2EDK-02988 entitled “Monitoring of the environmental fingerprint in Graviera Naxou PDO product for certification of authenticity and geographical origin”) 511