Introduction: Recent studies have reported improved gain, feed efficiency and protein retention when pigs are fed higher levels of soybean meal (SBM). The mechanism may be due to increased utilization of amino acids from SBM, which differ in absorption patterns from synthetic amino acids (SAA). 

Objective: To compare the plasma amino acid responses (PAAs) in pigs fed intact protein sources (SBM or corn-DDGS) and SAA additions. Materials and 

Methods: PAAs were measured in two growing pig studies. Experiment used 10 pigs (average 20.2 kg) in a cross-over design. Venous catheters (18 ga., 8 cm) were inserted in the jugular vein 2 days prior to receiving supplement (SUPP). Four supplements were formulated to SBM or DDGS with either low or high levels of a synthetic amino acid (AA) blend, all fed to provide 5 g of SID lysine in a meal. AA provided 4 g of lysine and a profile of methionine, threonine, tryptophan and valine consistent with an ideal amino acid concept (NRC, 2012). The supplements were provided immediately prior to sequential collection of blood samples at 0, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 hrs. Experiment II used a sub-sample of 1 blood sample per pen (15 per treatment, 6 pigs per pen) from a total of 540 pigs (PIC X Duroc) weaned at 21 days of age (5.3 kg) to market (125 kg). Six dietary treatments consisting of high, medium and low SBM levels altered with the utilization of 0.5%, 0.25% and no added lysine in either a corn-SBM or corn-DDGS based diet formulation were utilized. 

Results and Discussion: In both Exp. I and II, SUPP or Diet dramatically altered individual essential AAs (P < 0.01). Post-prandial PAA responses to SBM+AA increases the peak PAA levels (Lys, Thr, Met, and Val) by 90 min after ingestion vs SBM (P < 0.01). SBM increased plasma levels of (Trp, His, Iso, and Leu and NEAA’s) from 90 to 210 min vs SAA (P < 0.01). DDGS ingestion did not raise PAA nor sustain levels of PAA’s similar to SBM. 

Conclusion: The PAA response to SBM was slower and sustained to 210 minutes post-ingestion. Future research should extend the collection period. AA increases the PAA response of the supplemented AA and reduces the levels of non-supplemented AA in SBM. The length of time and array of essential AA elevated in circulation may partially explain the increase in N and protein retention in pigs fed intact SBM vs higher levels ( > 0.25% of diet) of AA.

Olson, L., J. Halbur, J. Hong, R. Samuel, R. Thaler, E. Weaver, A. Framer and F. Urschel. 2025. The effects of soybean meal, DDDGS and amino acid supplementation on plasma amino acids in growing pigs. 2025 American Society of Animal Science Midwest Section meeting, Abstract 100.