Effect of kind of dietary fat on the quality of milk fat from Italian Friesian cows

Four diets, supplemented with different fats of vegetable origin, were compared in a 4 X 4 Latin square design with eight primiparous Italian Friesian cows (two cows per cell). The four fats were: toasted full fat soy bean in diet WS; toasted full fat linseed in diet WL; calcium soap of palm oil in diet PS; and calcium soap of olive oil in diet OS. Scope of the trial was to study the effect of the four different fat sources on milk yield and composition and on the quality of milk fat in terms of safety for the consumer health, with particular attention to trans fatty acids and to conjugated linoleic acid isomers (CLA). Diet OS induced the highest milk yield (P < 0.05), while diet PS gave the fattest milk (P < 0.05), and the highest milk content of both saturated and medium chain fatty acids (P < 0.05). Saturated to unsaturated ratio of milk fat was decreased when cows were fed diet WS (P < 0.05), while the ratio was increased with cows fed on diet PS (P < 0.05). With a closely similar behaviour milk CLA content was enhanced with diet WS and strongly depressed (P < 0.05) with diet PS. Diet OS increased total CLA as well, probably as a consequence of the bio-hydrogenation process of large amounts of oleic acid, transformed into trans isomers of C-18:1, including vaccenic acids. Full fat soy bean promoted some milk fatty acids with beneficial effects on consumer health, but calcium soap of olive oil similarly improved the fatty acid profile of milk fat, while meeting the cows' requirements as an energy supplement. (C) 2003 Elsevier B.V. All rights reserved.