Oxidative status of dairy cows fed flax meal and infused with sunflower oil in the abomasum

Flax products increase concentration of antioxidants in milk and plasma of dairy cows, which may reduce oxidative damage resulting from lipoperoxidation of polyunsaturated fatty acids. The aim of this study was to investigate the effects of flax meal on the antioxidant status of dairy cows infused with sunflower oil (SO), a source of omega-6 fatty acids (FA), in the abomasum. Eight rumen fistulated lactating Holstein cows were assigned to a double 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments: (1) control diet with no flax meal and no infusion of SO (CO); (2) diet containing 137 g/kg flax meal (FM); (3) CO and infusion of 250 g SO/d; and (4) FM and infusion of 250 g SO/d. Dry matter intake and milk production were similar among diets. Flax meal increased milk fat concentration. Dietary FM supplementation increased plasma concentration of saturated fatty acids, and tended to reduce the polyunsaturated to saturated FA ratio. The plasma peroxidizability index was not affected by FM supplementation or SO infusion. Infusion of SO increased antioxidant capacity and rate of diene production, and decreased the time to reach maximal amount of conjugated diene production in plasma. Production of thiobarbituric reactive substances (TBARS) in ruminal fluid was reduced by dietary FM. Milk and plasma TBARS production were not affected by FM supplementation. Sunflower oil had no effect on TBARS production in ruminal contents, milk and plasma. In conclusion, feeding FM to dairy cows receiving a source of omega-6 FA (250 g/d) that bypasses the rumen did not protect cows and milk from lipoperoxidation.