Two studies were conducted to estimate the SID Lys requirement for growth and feed efficiency of 70-130-kg DNA finishing pigs. In Exp. 1, 616 pigs (600×241, DNA; initially 76.4±1.25 kg) were used from 70-100-kg and in Exp. 2, 679 pigs (600×241, DNA; initially 103.8±1.32 kg) were used from 100-130 kg. Pens of pigs were blocked by BW and randomly allotted to dietary treatments with 8-10 pigs/pen in a randomized complete block design. Diets were corn-soybean meal based and SID Lys increased by

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... easing soybean meal and feed-grade amino acids while maintaining minimum ratios for other amino acids. From 70-100 kg, ADG, G:F, Lys intake/d, and Lys intake/kg of gain all increased, (linear, P < 0.05) with increasing SID Lys. From 100-130 kg, ADG, Lys intake/d, and Lys intake/kg of gain increased (linear, P < 0.05) with increasing SID Lys, while G:F increased (quadratic, P = 0.032). At current ingredient and pig prices, there were no statistical differences in income over feed cost (IOFC) from 70-100 kg. From 100-130 kg, increasing SID Lys increased (quadratic, P = 0.001) IOFC. A broken-line linear (BLL) model predicted optimal ADG at 0.83% SID Lys, while a quadratic polynomial (QP) model predicted a requirement of 0.90% for G:F from 75-100 kg. A QP model predicted maximum IOFC at 0.78% SID Lys from 75-100 kg. From 100-130 kg, BLL models predicted optimal ADG and G:F at 0.64 and 0.59% SID Lys, respectively. A QP model predicted maximum IOFC at 0.64% SID Lys. In summary, these results suggest the optimal SID Lys level for 75-100 kg DNA finishing pigs for growth performance is between 0.83 and 0.90% SID Lys, and 0.78% SID Lys for maximum IOFC. The optimal SID Lys level in 100-130 kg DNA finishing pigs depends upon the response criteria, with growth performance and IOFC maximized between 0.59 and 0.64% SID Lys.