The main goal of this work was to describe a natural variation of stable isotope ratio in a cow’s, goat and sheep dairy products from Slovenian geographical macroregions. Cow’s milk showed significant difference in the distribution of δ13Ck and δ15Nk in four regions (p ⡤ 0.05). The highest average values were determined in Pannonian region, the lowest in Mediterranean region, while Alpine and Dinaric region showed a great deviation in δ13Ck and δ15Nk values. Milk samples from goat and sheep milk showed smaller deviation in δ13Ck and δ15Nk than cow’s milk among the macroregions. Goat, sheep cheeses and cheese Tolminc didn't show significant difference in δ13Ck and δ15Nk values. Isotopic values of cheese Tolminc were distributed in a small interval, which might reflect geographic condition of upper Soča river region. Cow's milk compared with sheep and goat milk showed significant difference in the distribution of δ13Ck, δ15Nk and δ18O values (p ⡤ 0.05). These differences might originate from use of different farming system, enrichment of water due to evaporation and different sampling system. With cross classification tests 47.8% of cow's, 71.4% of sheep and 66.7% of goat milk samples were correctly classified according to Slovenian macrogeographic region. Milk samples from bovine, goat and sheep species were correctly classified in 82.9%. The results indicate that stable isotopes of bio-elements in dairy products can only partly distinguish between samples from different origin and animal species.
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