Concentrations of digestible amino acids in co-products from threonine and tryptophan fermentation are greater than in soybean meal

An experiment was conducted to test the hypothesis that the standardized ileal digestibility of crude protein (CP) and amino acids (AA) in threonine biomass (Thr-BM) and 2 sources of tryptophan biomass (Trp-BM1 and Trp-BM2) were greater than in soybean meal (SBM). Twelve weanling barrows (11.08 ± 1.06 kg) that had a T-cannula installed in the distal ileum were allotted to a replicated 6 × 6 Latin square design with 6 diets and 6 periods. A nitrogen-free diet, a diet based on SBM, and a diet based on a combination of SBM and Thr-BM were formulated. Two additional diets were formulated based on a combination of SBM and the 2 sources of tryptophan biomass. The last diet was not related to this work. Diets were fed to pigs for 7 days, and ileal digesta were collected on days 6 and 7 of each period. Results indicated that concentrations of CP and AA were greater in biomass products than in SBM, and the AID of threonine was greater (P < 0.01) in the diet containing Thr-BM than in the SBM diet or the diets containing Trp-BM1 or Trp-BM2. The AID and SID of tryptophan were greater (P < 0.01) in diets containing Trp-BM1 or Trp-BM2 than in the SBM diet or Thr-BM diet. The AID and SID of aspartate were also greater (P < 0.01) in Trp-BM1 and Trp-BM2 than in Thr-BM. However, the AID and SID for all other AA in Thr-BM were not different from Trp-BM1 and Trp-BM2. The quantities of standardized ileal digestible CP and AA were also greater (P < 0.01) in biomass products compared with SBM. In conclusion, concentrations of standardardized ileal digestible CP and most AA in biomass products were greater than in SBM. Therefore, these biomass products may be used to replace other protein sources in diets fed to weanling pigs, but further research is needed to determine digestibility of energy and other nutrients, optimal inclusion rates, and effects of biomass products on pig growth performance and health.