The objectives of this study were to test the influence of a recently developed rumen protected feed supplement containing extruded linseed meal and fish oil (LFO), which was fed to lactating Holstein-Friesian cows for 10 weeks at the rate of 800 g day 1 per animal, on the chemical and fatty acid (FA) composition of raw and ultra-high temperature (UHT) treated milks and to evaluate changes in sensory properties of UHT milk by both instrumental analysis and a panel of human assessors. Inclusion of LFO in the diet did not affect milk yield or the protein and fat contents of raw and UHT milks; however, it improved the FA composition of the milk fat by increasing the concentrations of health-enhancing polyunsaturated FA and beneficially decreasing the n-6/n-3 FA ratio without adversely affecting the sensory properties of the final product (UHT milk