Infl uences of high alpine hypoxia, of an alpine forage-only diet and of a typical alpine feed quality on milk fat composition of dairy cows were tested at two altitudes (400 and 2000 m a.s.l.) with two hay types one originating from lowlands one from highlands and fed at both altitudes. Hypoxia caused reduced proportions of n-3 fatty acids, particularly α-linolenic acid, in milk fat but the alpine feeding regime increased proportions of all n-3 fatty acids and CLA to a much greater extent. Feeding alpine hay decreased the proportion of the saturated fatty acids in milk fat.