Amino acid digestibility in soybean meal and crystalline amino acid based diets fed to growing pigs

Soybean meal (SBM) is the major source of amino acids (AA) and energy in diets for swine throughout the world. However, due to the emergence of feed-grade crystalline AA, it is estimated that SBM usage by pigs has been reduced by at least 35% over the last 25 years. Reduction on concentration of SBM and increasing the use of crystalline AA in diets may impact the digestibility of crude protein (CP) and AA. Therefore, the objective of this experiment was to test the hypothesis that diets containing corn, SBM, and crystalline AA have greater AA digestibility compared with corn and SBM diets.


Material and methods

Seven diets were formulated, and conventional corn and SBM were used (Table 1). The first diet contained 70% corn, 27% SBM, and no CAA. Diet 2 was similar to a typical commercial diet containing 77% corn, 19% SBM, crystalline Lys, Met, and Thr. Diet 3 contained 80% corn, 17% SBM, and CAA. Diet 4 contained 82% corn, 14% SBM, and CAA. Diet 5 contained 84% corn, 12% SBM, and CAA. Diet 6 contained 86% corn, 9% SBM, and CAA. Diets 3 to 6 had reduced protein of 1, 2, 3, and 4% units and greater CAA inclusion compared with the second diet. Diet 7 was a N-free diet that was used to determine basal endogenous losses of CP and AA. Seven barrows (initial body weight: 38.2 ± 1.5 kg) that had a T-cannula installed in the distal ileum were used. Pigs were allotted to a replicated 7 × 7 Latin square design with 7 diets and 7 periods for a total of 7 observations per treatment. The initial 5 d of each period was considered an adaptation period. Ileal digesta were collected on d 6 and 7 for 9 h using standard procedures. Diets and ileal digesta samples were analyzed for AA and Cr to calculate digestibility values.



The standardized ileal digestibility (SID) of CP increases (P < 0.01) as inclusion of crystalline AA increases in the diets, and this effect was also observed for SID values of AA (except Leu; Table 2). The observed increase in SID of AA in diets containing crystalline AA is likely due to the fact that crystalline AA are almost totally absorbed in the small intestine. Less SBM inclusion also indicates reduced antinutritional factors (e.g., trypsin inhibitors and oligosaccharides), which may influence digestibility of AA. No differences in SID of CP and AA were observed (except Met and Trp) between the commercial diet and the corn-SBM diet with no crystalline AA, which indicates that a certain amount of crystalline AA is needed to increase SID of AA in pig diets.



  • Inclusion of crystalline AA increased SID of CP and AA in pig diets.
  • There was no difference on SID of CP and AA (except Met and Trp) between a corn-SBM with no CAA diet and commercial corn-SBM with CAA inclusion.
  • A certain inclusion of CAA may be necessary to significantly increase the SID of AA in corn-SBM diets for growing pigs.


Table 1. Analyzed composition of ingredients, as-fed basis


Table 2. Standardized ileal digestibility of CP and AA in diets with crystalline AA by growing pigs1,2

1Each least squares mean for experimental diets from growing pigs represents 9 observations, respectively.

2Values for SID were calculated by correcting the values for AID for the basal ileal endogenous losses. The basal ileal endogenous losses were determined (g/kg DMI) as CP, 18.45; Arg, 0.82; His, 0.23; Ile, 0.36; Leu, 0.62; Lys, 0.81; Met, 0.09; Phe, 0.41; Thr, 0.62; Trp, 0.12; Val, 0.44; Ala, 0.77; Asp, 0.88; Cys, 0.22; Glu, 1.06; Gly, 2.14; Ser, 0.60; and Tyr, 0.30.


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