Effects of Increasing Soybean Meal and Valine:Lysine and Tryptophan:Lysine Ratios on Finishing Pig Performance

A total of 621 pigs (DNA 241 × 600; initially 138.0 ± 5.5 lb) were used in a 65-d growth trial to determine the effect of increasing soybean meal (SBM) and Val:Lys and Trp:Lys ratios on finishing pig performance. Experimental diets were corn-soybean meal-DDGS-based and fed in 3 phases. The 6 dietary treatments were arranged in a 3 × 2 factorial with main effects of SBM level (low, medium, high) and Val:Lys and Trp:Lys ratios (standard and high). The additional amino acids (AA) provided by increasing levels of SBM in diets with standard AA ratios were expected to result in a higher ADG by balancing out the high leucine from corn. Conversely, ADG was expected to stay the same as SBM increased when the Val:Lys and Trp:Lys ratios in the feed were increased. Pens of pigs were assigned to treatments in a randomized complete block design with BW as a blocking factor. There were approximately 8 or 9 pigs per pen and 12 replicate pens per treatment. No evidence (P \u3e 0.05) of SBM × AA ratio interactions or treatment differences were observed for any response criteria for phases 1 and 2 of the study. In phase 3, a marginally significant (P = 0.084) SBM × AA ratio interaction was observed for ADG. The medium level of SBM with standard Val:Lys and Trp:Lys ratios resulted in greater (quadratic, P = 0.003) ADG compared to other SBM levels. No differences in ADG were observed with increasing SBM when Val:Lys and Trp:Lys ratios were increased (P = 0.501). Additionally, F/G improved (quadratic, P = 0.007) at the medium level of SBM in phase 3. In spite of the improvement observed in phase 3, there were no significant differences (P \u3e 0.10) observed in overall ADG or ADFI. A marginally significant (P = 0.052) SBM × AA ratio interaction was observed for overall F/G. Increasing SBM in diets with greater Val:Lys and Trp:Lys ratios resulted in poorer (P = 0.049) F/G. There was no difference (P = 0.435) in F/G observed with increasing SBM in feeds with standard Val:Lys and Trp:Lys ratios. In conclusion, in early finishing there were no responses to increasing SBM; however, in the late finishing period when diets included 0, 4, or 8% SBM, pigs fed 4% SBM diets with standard BCAA ratios had improved ADG and F/G. Throughout the study, increasing Val:Lys and Trp:Lys ratios had little effect on pig performance