Seasonal Variation of Δ¹⁸O, Δ¹³C and Δ¹⁵N in Cow's Milk

Dairy products are of particular interest as a group of foods that play an important role in feeding the human population. The composition of milk is dependent upon the feed supplied to dairy cows, and as a consequence, especially for grazing cattle, on their particular environment. To better understand the temporal variation of δ ¹⁸O, δ ¹³C and δ ¹⁵N values in milk from a single environment, measurements of stable isotope ratios in cow's milk water were compared to, artesian water, precipitation and the stable isotope values of the forage and feed. The main water source for the cow was artesian water during the winter, while during the summer grass water influenced oxygen stable isotope values in the milk water. Stable oxygen isotope ratios in milk water were relatively lower in winter/transitional seasons and higher in summer showing the dependence on the main water source, meanwhile δ ¹³C and δ ¹⁵N values reflected the particular season's food source. (author)