Fatty acid content in milk of dairy cows on a diet with high fat content derived from rapeseed

Two groups of dairy cows, Czech Red-pied x Ayrshire x Red Holstein crossbreds, received a diet with either production mixture with rapeseed, rapeseed cakes and rapeseed oil (Energol; E-group; final feed mixture with 62 g of crude fat per kg of dry matter, DM) or control production mixture (C-group; crude fat content in total feed mixture 37 g/kg DM). Milk samples were taken on the 14th, 30th, 60th and 90th day of lactation, and basic milk constituents and fatty acid content in milk fat were determined. E- and C-groups did not differ in either milk yield or yield of milk fat, milk protein and lactose (P > 0.05). Lactose, calcium, milk protein and casein content increased linearly (P < 0.05) with the increasing day of lactation both in E-milk and in C-milk. Casein content in E-milk was lower (P < 0.05) than in C-milk but total lipid content did not differ (P > 0.05) from that in C-milk. Dietary rapeseed decreased (P < 0.05) palmitic acid content in milk by 20 percentage units and at the same time increased (P < 0.05) oleic acid content by 10 percentage units in comparison with control milk; the ratio of total C16/total C18 fatty acids was consequently twice lower (P < 0,01) in E-milk. As far as polyunsaturated fatty acids (PUFA) are concerned, the contents of linoleic acid (LA), a-linolenic acid (LNA) and eicosapentaenoic + docosahexaenoic acid were higher (P < 0.05) in E-milk; however, the PUFAn-6/PUFAn-3 ratio was not different between E- and C-milk. It was concluded that I litre of E-milk could provide 20% of both LA and LNA daily requirement.