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 > 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 > 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.