Effect of flax meal on the production performance and oxidative status of dairy cows infused with flax oil in the abomasum

• Flax products have strong antioxidant properties.
• Omega-3 rich diets increase lipid peroxidation in tissues of dairy cows.
• Flax meal does not prevent lipoperoxidation in cows fed omega-3 rich diets.

Rumen bypass of flax oil (FO), which is rich in omega-3 fatty acids (FA), contributes to increase polyunsaturated FA proportion in milk fat. Flax meal (FM) is a source of antioxidants, which may reduce oxidative damage in cows given omega-3 FA. The aim of this study was to investigate the effects of dietary FM supplement on performance and antioxidant status in dairy cows infused with FO 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 FM (CO); (2) diet containing 124 g/kg FM in the dry matter (DM); (3) CO and 250 g FO/d infused in the abomasum; and (4) FM and 250 g FO/d infused in the abomasum. Intake of DM and total DM input (including abomasally infused oil) were increased for cows fed FM and reduced for cows infused with FO. Milk production and milk composition did not differ among treatments except for lactose concentration that was increased with FO infusion. Milk fat from cows fed FM had lower omega-6 FA proportions. Abomasal infusion of FO increased proportions of polyunsaturated, omega-6 and omega-3 FA in milk fat. Cows fed CO with no FO infusion showed higher omega-6/omega-3 FA ratio in milk fat compared with the other treatments, whereas no difference was observed between CO and FM when FO was infused in the abomasum. Feeding FM did not change plasma and milk thiobarbituric acid reactive substances concentrations, whereas FO increased them. Infusion of FO in the abomasum increased the peroxidizability index, the maximal conjugated diene (CD) production and rate of CD production, whereas lag time and time to reach maximum amount of CD were reduced. Plasma antioxidant capacity before feeding was increased when cows received dietary FM or FO abomasal infusion, whereas no differences were observed 3 h postfeeding. Results suggest that FM supplementation to dairy cows receiving a source of polyunsaturated FA that bypasses the rumen does not provide any benefits for protecting cows and milk against lipoperoxidation.