The effect of sunflower oil on the fatty acid composition of the milk of Cows fed either a fat‐depressing diet or grass silage

Two experiments have been carried out in which different forms of sunflower oil were added to the diet of Ayrshire heifers. In experiment 1, the animals were given a fat‐depressing diet of dried, ground grass cubes and flaked maize. When either free sunflower oil or milled, unextracted sunflower seeds were added to this diet, the yield of milk fat and of all fatty acids up to 16:1 was decreased and the yield of all 18‐carbon fatty acids was slightly increased. When the sunflower oil was protected by encapsulation in formaldehyde‐treated casein, the yield of milk fat was increased, that of the fatty acids up to 16:1 was decreased and that of all the 18‐carbon fatty acids, and in particular, of the polyunsaturated fatty acids was increased. In experiment 2, the animals were given a basal diet of grass silage and concentrates to which increasing amounts of protected sunflower oil were added. This tended to increase the yield of milk fat and to reduce that of the fatty acids up to 16:1. The yield of all the 18‐carbon fatty acids increased and, in particular, that of the polyunsaturated fatty acids increased progressively as more protected oil was added. It is concluded that it should be possible to produce a milk with any desired proportion of polyunsaturated fatty acids by adding a predetermined amount of protected oil to the diet of the cow.