The objective of our study was to determine the effects of abomasal infusion of an emulsifier on fatty acid (FA) digestibility and production responses of lactating dairy cows. Eight rumen-cannulated cows (109 ± 18 d in milk) were randomly assigned to a treatment sequence in replicated 4 × 4 Latin squares with 18-d periods including 7 d of washout and 11 d of infusion with sampling on the last 4 d. Treatments were abomasal infusions of water carrier only (CON) and 3 levels of increasing doses of Tween 80 (polysorbate 80, Tween 80, Sigma-Aldrich, St. Louis, MO) delivering 15 (D-15), 30 (D-30), and 45 (D-45) g/d. The Tween 80 was dissolved in water before infusions, which were delivered at 6-h intervals. Cows were fed the same diet, which contained (% dry matter) 31% neutral detergent fiber, 17% crude protein, 25% starch, and 4% FA (2% dry matter from a saturated fat supplement containing 33% C16:0 and 51% C18:0). Increasing emulsifier infusion dose quadratically increased digestibility of total FA (60.7, 65.3, 70.9, and 66.8%), 16-carbon FA (61.7, 63.9, 70.4, and 66.7%), and 18-carbon FA (59.8, 65.6, 71.1, and 66.6%, respectively). Increasing emulsifier infusion dose quadratically increased absorbed total FA (625, 670, 744, and 658 g/d), 16-carbon FA (151, 157, 197, and 157 g/d, quadratic), and 18-carbon FA (420, 460, 500, and 444 g/d). Increasing emulsifier infusion dose tended to quadratically decrease dry matter intake (29.0, 28.8, 29.6, and 27.6 kg/d). Increasing emulsifier infusion dose quadratically increased milk fat content (3.23, 3.35, 3.45, and 3.35%), milk fat yield (1.54, 1.61, 1.65, and 1.55 kg/d), ECM (45.7, 46.9, 47.5, and 45.3 kg/d), and plasma nonesterified fatty acid concentration (95.6, 98.4, 101.2, and 98.6 μEq/L). On a yield basis, we observed that de novo, mixed, and preformed FA responded quadratically to Tween 80 infusion due to FA yield increasing up to D-30. Treatments had no effect on milk yield (47.9, 48.3, 48.0, and 46.6 kg/d). In conclusion, short-term infusion of an exogenous emulsifier improved FA digestibility and milk fat yield responses when cows were fed a diet containing a saturated fat supplement. Most digestion and production measurements responded quadratically because the highest dose of exogenous emulsifier (45 g/d) decreased dry matter intake and performance.