Twenty-four Holstein cows were used in a randomized complete block design to test the efficacy of clay, MYCOAD, in reducing aflatoxin M₁ (AFM1) in milk. Cows were blocked by parity and stage of lactation. Cows were housed in a freestall barn with sand bedding and were fed and milked twice daily. Cows were adapted to individual feed gates (Calan Broadbent Feeding System, American Calan, Northwood, NH) one week before the treatment period. The experiment consisted of a 7 d treatment period. Cows were randomly assigned one of 4 dietary treatments (n = 6): (1) control (CON) TMR; (2) aflatoxin (AF) TMR contaminated with 300ppb aflatoxin B₁ (AFB1); (3) adsorbent diet (MYC) TMR containing 50 g of clay/cow/day; (4) AF diet with clay (AF+MYC) contaminated with 300ppb AFB1 containing 50 g of clay/cow/day. All additions to TMR were topdressed. Data were analyzed using the MIXED procedure of SAS (Cary, NC). Main effects were treatment, days in milk, parity, and day. All interactions were tested and backward stepwise elimination was used to remove nonsignificant interactions. Significance was declared at P < 0.05. Dry matter intake (DMI) was similar across treatments. Cows consuming CON produced less milk compared with cows on other treatments (29.0 v. 36.1 kg/d; P < 0.01). Cows consuming CON were less efficient compared with cows on other treatments (0.81 v. 1.71 kg DMI/kg milk). This decrease in efficiency of CON cows was likely due to the decrease in MY. Although milk components (%) were similar across treatments, yields (kg) of protein and solids were less in cows fed CON diets. Protein yield averaged 0.85, 1.12, 1.08, and 1.09 kg/d (P < 0.02), and solids yield averaged 2.53, 3.13, 3.06, and 3.24 kg/d for CON, AF, MYC, and MYC+AF respectively. Milk from cows fed AF had the greatest concentration of AFM1 (P < 0.001), and concentrations averaged 0.24, 2.26, 0.15, and 0.83 for CON, AF, MYC, and MYC+AF respectively. Cows fed AF+MYC averaged 1.43 ± 0.30 ppb AFM1 less than cows fed AF, resulting in a 63% reduction. Results from this study show that adding MYCOAD to contaminated diets was effective at reducing AFM1 concentrations in the milk of cows fed AFB1 without negatively affecting DMI, milk yield or feed efficiency.