Fat-corrected milk and ECM had positive linear treatment effects as concentration of adsorbent in the diet increased (P = 0.04 and 0.05, respectively). There were no treatment differences (P > 0.16) in feed efficiency (FCM/DMI, ECM/DMI, and milk yield/DMI) for the contrast (POS vs. CON), linear, or quadratic effects. Protein yield (kg/d) had a quadratic treatment effect (P = 0.01).