Twelve lactating Holstein cows with live body weight from 550 to 680 kg averaging 600 ± 15 kg and at 1-4 of lactation seasons were used in Latin square design (3x3) with three treatments and three successive experimental periods. Cows in G1 were fed the basal ration consisted of (on DM basis) 57.7% concentrate feed mixture (CFM) + 24.7% corn silage (CS) + 17.6% alfalfa hay (AH) without supplementation and served as a control. While, in G2 and G3, 1 and 0.5 kg soybean meal was replaced by 125 and 62.5 g Optigen™ plus 2.710 and 1.355 kg corn silage/ head/ day, respectively. Results showed that the contents of DM, OM, CP, NFC and NFE in experimental rations tended to decrease, however, the contents of CF, NDF, ADF and ash tended to increase with increasing the level of Optigen supplementation. The digestibility coefficients of all nutrients and nutritive values were not significantly affected by Optigen supplementation.  Average daily intake of total DM, TDN, CP, DCP, DE, ME and NEL were nearly similar for the different experimental rations. Moreover, average daily yield of actual milk and 4% FCM,  milk composition, the concentrations of urea and urea-N in milk, the concentrations of urea-N and total protein in blood plasma, feed conversion ratio, daily feed cost, feed cost /kg milk and economic efficiency were not affected significantly (P>0.05) by Optigen supplementation.  It could be concluded that optigen supplementation for lactating Holstein cows did not showed any significant effects on feed intake, digestibility, milk yield and composition along with feed conversion ratio and economic efficiency.