Milk fatty acid composition in response to reciprocal combinations of sunflower and fish oils in the diet

This study investigated the hypothesis that a high linoleic acid vegetable oil fed in combination with a fish oil ruminal biohydrogenation modifier as a diet supplement would result in higher concentrations of vaccenic and rumenic acids in milk fat versus either fed alone. Four lactating cows were fed legume silage (600 g/kg diet DM) and a lactation concentrate (400 g/kg DM) supplemented with 30 g/kg diet DM of oil in a Latin square design with 3-week experimental periods. Fish oil was proportionately 0, 0.33, 0.67 or 1.0 of the oil supplement, with the balance as sunflower oil. The DM intake decreased linearly (P<0.04) with increasing concentrations of fish oil in the diet. Milk yield and its proportion of protein were unaffected by fish oil intake, whereas the proportion of milk fat increased linearly (P<0.02) with increasing fish oil. Proportions of milk fatty acids from C4 to 16:1 increased linearly (P<0.01) for all fatty acids except 14:1 (NS) as the proportion of fish oil increased. Conversely, 18:0 (0.001), cis-9 18:1 and 18:2 (P<0.01) decreased linearly with increasing fish oil, while trans-11 18:1 and cis-9, trans-11 18:2 were highest at intermediate levels of fish oil. Other identified trans isomers declined as fish oil increased. Arachidonic acid (AA; P<0.001), eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA; P<0.01) increased linearly in milk fat with increased fish oil feeding, whereas predictions were less robust for docosahexaenoic acid (DHA; P<0.05). Efficiency of transfer of fish oil fatty acids to milk fat, estimated by regressing their milk output on intake, ranged from <0.01 for DHA (P<0.10) to 0.79 for AA (P<0.01). Whereas only 10 mg of DHA/g intake appeared in milk, transfer of EPA was 57 mg/g intake (P<0.04) and for DPA it was 110 mg/g (P<0.01). Supplementing high linoleic vegetable oils with fish oil maximized concentrations of vaccenic and rumenic acids in milk fat, and transfer of eicosanoic fatty acids from diet to milk increased linearly as their intake increased.