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Two studies were conducted to estimate the SID Thr:Lys requirement for growth and feed efficiency of PIC 337×1050 pigs from approximately 12- to 70-kg. In Exp. 1, 987 pigs [initial body weight (BW) = 11.8±0.32 kg] were used from 12- to 24-kg. In Exp. 2,875 pigs (initial BW = 43.4±0.58 kg] were used from 43- to 70-kg. Pens of pigs were blocked by BW and randomly allotted to dietary treatments in randomized complete block designs, with 21 to 27 pigs per pen with 8 and 7 replications per treatment (Exp. 1 and 2, respectively). Pens were provided 1 of 5 dietary treatments with increasing SID Thr:Lys ratios at 53, 58, 62, 65, and 68% in each experiment. Two corn-soybean meal-based diets containing 53 and 68% Thr:Lys ratios were blended to achieve target SID Thr:Lys treatment levels in each experiment. In Exp. 1 (12- to 24-kg), ADG and final BW increased (linear, P = 0.006) while ADFI, G:F, Thr intake/d, and Thr intake/kg of gain increased (quadratic, P = 0.001) as Thr:Lys ratio increased (Table). Additionally, Lys intake/d increased (quadratic, P < 0.001) while Lys intake/kg of gain decreased (quadratic, P < 0.001) with increasing Thr:Lys ratio. In Exp. 2 (43- to 70-kg), ADG, G:F, final BW, Thr intake/d and Thr intake/kg of gain also increased (linear, P = 0.036) as dietary Thr:Lys increased. Moreover, Lys intake/kg of gain decreased (linear, P = 0.023) with increasing Thr:Lys. A quadratic polynomial (QP) model predicted a requirement at levels greater than 68% SID Thr:Lys for ADG from 12- to 24-kg, while a QP model suggested that maximum G:F was achieved at 61.8% SID Thr:Lys (Exp. 1). From 43- to 70-kg, QP models suggested maximum ADG and G:F were achieved at levels greater than 68% SID Thr:Lys (Exp. 2). However, similar fitting BLL models predicted no further improvement to G:F and ADG beyond 65 and 67% SID Thr:Lys, respectively. In summary, these results suggest the optimal SID Thr:Lys for 12- to 24-kg pigs is 61.8% for feed efficiency and greater than 68% for ADG. From 43- to 70-kg, the requirement was predicted at or above 65 and 67% SID Thr:Lys for G:F and ADG, respectively. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate growth performance and economic return of PIC 800 × Camborough pigs fed increasing SID Lys from approximately 12- to 136-kg. Pens of pigs were blocked by body weight (BW) and randomly assigned to 1 of 5 dietary treatments in a randomized complete block design with 26 pigs per pen and 16 pens per treatment. Pens were provided 1 of 5 dietary treatments with increasing SID Lys at 85, 93, 100, 107, and 115% of current (2021) PIC recommendations within 6 dietary phases as follows: phase 1 (1.09, 1.19, 1.28, 1.36, and 1.47%), phase 2 (0.97, 1.06, 1.14, 1.22, and 1.32%), phase 3 (0.87, 0.95, 1.02, 1.09, and 1.17%), phase 4 (0.75, 0.82, 0.88, 0.94, and 1.01%), phase 5 (0.66, 0.72, 0.77, 0.82, and 0.89%), and phase 6 (0.59, 0.64, 0.69, 0.74, and 0.79%). Two corn-soybean meal-based diets containing low and high Lys were blended to achieve target SID Lys levels for each treatment diet within phase. Overall (d 0 to 143), increasing SID Lys improved (linear, P = 0.007) ADG and G:F, but did not impact ADFI (P > 0.10; Table). A tendency (linear, P = 0.067) for heavier hot carcass weights (HCW) was observed in pigs fed increasing SID Lys. However, there was no evidence for differences (P > 0.10) in carcass yield, backfat depth, loin depth, or carcass lean percentage across treatments. The linear (LM) model served as the best fit for both growth and economic parameters. The LM model predicted maximum ADG and G:F at levels greater than 115% of PIC's current recommendations. However, for income over feed cost (IOFC), the LM model predicted maximum profitability at or below 85% of the current Lys recommendations of PIC. In conclusion, the optimal SID Lys level for PIC 800 × Camborough pigs from 12- to 136-kg differed upon response criteria, with growth performance maximized at levels at or above 115% of the recommendation for SID Lys by PIC; however, maximal economic returns were observed at or below 85% of PIC's current SID Lys recommendations. [ABSTRACT FROM AUTHOR]