We evaluated the long-term effects of feeding a C16:0 supplement (85% C16:0) on production responses of primiparous and multiparous mid-lactation dairy cows. Forty Holstein cows (144 ± 44 DIM; 18 primiparous and 22 multiparous) were blocked by parity, milk production, and BCS, and assigned to either a control diet containing no supplemental fat (CON) or a C16:0 supplemented diet (PA; 1.5% diet DM) for 10 wks. PA replaced soyhulls and diets contained (% DM) 21% forage NDF, 17% CP, and 27% starch. After the treatment period, all cows received the CON diet for 2 wks to evaluate carryover effects. The statistical model included the random effect of block and cow within parity, and the fixed effect of treatment, parity, time, and their interactions. During the 10-wk treatment period, compared with CON, PA consistently increased DMI (31.0 vs. 29.5 kg/d; P < 0.01), milk yield (49.4 vs. 45.6 kg/d; P < 0.01), milk fat content (3.35 vs. 3.15%; P < 0.01), milk fat yield (1.56 vs. 1.41 kg/d; P = 0.03), yield of 16-carbon milk FA (582 vs. 453 g/d; P < 0.01), ECM (47.1 vs. 43.4 kg/d; P = 0.01), feed efficiency (3.5% ECM/DMI; 1.52 vs. 1.47; P = 0.05) and tended to increase milk protein yield (1.40 vs. 1.31 kg/d; P = 0.06). There was no effect of treatment on the yield of de novo milk FA (318 vs. 342 g/d; P = 0.37), yield of preformed milk FA (555 vs. 549 g/d; P = 0.84), BW (698 vs. 689 kg; P = 0.71), or BCS (3.26 vs. 3.31; P = 0.65). Treatment by parity interactions were observed for ECM (interaction, P = 0.08), and milk fat yield (interaction, P = 0.05) due to PA increasing these variables to a greater extent in multiparous than primiparous cows. In contrast, compared with CON, PA increased BW change in primiparous, but not in multiparous cows (interaction, P = 0.09). During the carryover period, compared with CON, PA tended to increase ECM (42.2 vs. 40.4 kg/d; P = 0.07), and milk fat yield (1.33 vs. 1.28 kg/d; P = 0.07). In conclusion, production responses of dairy cows to C16:0 supplementation were consistent throughout the 10-wk treatment period, and had carryover effects on the yield of milk fat and ECM. Overall, C16:0 increased DMI, milk yield, milk fat yield, ECM, and feed efficiency in mid-lactation dairy cows.