Abomasal infusion of oleic acid and exogenous emulsifier alter fatty acid digestibility and production responses of lactating dairy cows.

We evaluated the effects of abomasal infusion of cis-9 C18:1 (oleic acid) and an exogenous emulsifier (polysorbate-C18:1) on fatty acid (FA) digestibility and production responses of dairy cows. Eight rumen-cannulated multiparous cows (96 ± 23 d in milk) were assigned to a 2 × 2 factorial arrangement of treatments in 4 × 4 Latin squares with 18-d periods consisting of 7 d of washout and 11 d of infusion. Treatments were abomasal infusions of water carrier only (CON), 45 g/d oleic acid (OA), 20 g/d polysorbate-C18:1 (T80), or both 45 g/d OA and 20 g/d T80 (OA+T80). The OA treatments were dissolved in ethanol and the T80 treatments in water. To deliver the daily dose for each treatment, the infusate solution was divided into 4 equal infusions per day, occurring every 6 h. Cows were fed the same diet, which contained [% of dry matter (DM)] 30.3% neutral detergent fiber (NDF), 16.3% crude protein, 30% starch, and 3.2% FA (including 1.8% DM from a FA supplement containing 34.4% C16:0 and 47.7% C18:0). Infusion of T80 increased NDF digestibility compared with all other treatments (3.57 percentage units), whereas OA+T80 decreased NDF digestibility compared with CON (3.30 percentage units). Compared with CON, OA (4.90 percentage units) and T80 (3.40 percentage units) increased total FA digestibility, whereas OA+T80 had no effect on total FA digestibility. We did not observe differences between OA and T80 for total FA digestibility. Infusion of OA (3.90 percentage units) and T80 (2.80 percentage units) increased 16-carbon FA digestibility compared with CON. Digestibility of 16-carbon FA did not differ between OA and T80 or between CON and OA+T80. Compared with CON, OA increased (5.60 percentage units) and T80 tended to increase 18-carbon FA digestibility. Digestibility of 18-carbon FA did not differ between OA and T80 or between CON and OA+T80. Compared with CON, all treatments increased or tended to increase the absorption of total and 18-carbon FA. Infusion of OA and T80 increased the yields of milk fat (both increased 0.10 kg/d), 3.5% fat-corrected milk (1.90 and 2.50 kg/d), and energy-corrected milk (1.80 and 2.60 kg/d) compared with CON. We did not observe differences between OA and T80 or between CON and OA+T80 for yields of milk fat, 3.5% fat-corrected milk, or energy-corrected milk. Infusing OA tended to increase plasma insulin concentration compared with CON. Compared with the other treatments, OA+T80 decreased the yield of de novo milk FA (31.3 g/d). Compared with CON, OA tended to increase the yield of de novo milk FA. Compared with OA+T80, CON and OA tended to increase the yield of mixed milk FA, whereas T80 increased it (83 g/d). Compared with CON, all emulsifier treatments increased the yield of preformed milk FA (52.7 g/d). In conclusion, abomasally infusing either 45 g of OA or 20 g of T80 improved digestibility and similarly favored the production parameters of dairy cows. In contrast, providing both (45 g of OA + 20 g of T80) had no additional benefits and moderated the positive responses observed in the individual treatments with OA and T80.