Comparing Increasing Tryptophan: Lysine Ratios in Distiller Dried Grains-Based Diets with or without Distiller Dried Grains withdrawal Strategy on Growth and Carcass Performance of Grow-Finish Pigs

Abstract A total of 6,240 pigs [DNA 600 × PIC 1050; initial body weight (BW) = 22.5 ± 0.20 kg], divided into 2 groups, were used in 119- or 120- day study comparing increasing Trp:Lys ratio in diets with DDGS or a DDGS withdrawal strategy on growth and carcass performance and carcass fat iodine value of grow-finish pigs. Pigs were randomly allotted to 1 of 7 dietary treatments with 30 to 36 pigs per pen and 26 replications per treatment. Diets were fed in 4 phases (approximately 23 to 44, 44 to 71, 71 to 104, and 104 kg to market). Diets included a control corn-soybean meal-based diet formulated to a 19% SID Trp:Lys ratio, 4 diets with 30% DDGS fed in all four phases and formulated to achieve 16%, 19%, 22%, or 25% SID Trp:Lys ratio, respectively, and 2 DDGS withdrawal strategy diets: 19% SID Trp:Lys with 30% DDGS in phase 1 through 3 and then in phase 4, 0% DDGS with either a 19 or 25% Trp:Lys ratio. Overall, BW, ADG, ADFI, and G:F increased (linear, P < 0.05) as SID Trp:Lys ratio increased in diets with 30% DDGS fed in all 4 phases (Table). Pigs fed diets containing a SID Trp:Lys ratio of 19% and 30% DDGS from phases 1 through 3 and 0% DDGS in phase 4 had the greatest numeric ADG and ADFI for the overall study, but was not different than pigs fed the control for ADG, or the 25% Trp:Lys withdrawal treatment and the 30% DDGS diets with 25% Trp:Lys ratio throughout the study for ADG and ADFI. Hot carcass weight and carcass yield increased (quadratic, P < 0.05) as Trp:Lys ratio increased. Carcass fat samples were taken from the loin-butt junction and analyzed for iodine value. Pigs fed the control diet had decreased (P < 0.05) carcass fat iodine value compared with pigs fed DDGS throughout the study, with pigs fed the two DDGS withdrawal strategies having decreased (P < 0.05) iodine values compared with pigs fed 30% DDGS in all 4 phases. In summary, increasing the SID Trp:Lys ratio in diets with 30% DDGS resulted in a linear improvement in ADG, ADFI, G:F, and BW but did not influence iodine values. Removing DDGS from the diet in the last period reduced carcass fat iodine value and increased growth rate during the withdrawal period compared with pigs fed 30% DDGS throughout, indicating value in a DDGS withdrawal strategy.