Recent research has reported higher net energy (NE) levels in soybean meal (SBM) compared to past loading values in the NRC (2012). Formulating diets to a lysine:energy ratio is a common method of adjusting the amino acid levels in diets containing varying energy levels. However, utilizing higher NE value levels of SBM in formulation could result in higher dietary lysine levels and higher diet cost if formulated for a constant ratio of Lysine:NE ratio. Also, SBM has slower amino acid release values than synthetic amino acids (Olson et al, 2024) which may enhance its utilization in the pig compared to the use of digestibility values. As SBM supply is increasing in South Dakota due to increased crush capacity, an opportunity exists for swine producers to re-evaluate the nutritional values of SBM for more cost-effective formulations. The objective of this experiment was to evaluate the impact of formulating to a lower lysine:NE ratio on pig performance in SBM and synthetic amino acid supplemented diets. A total of 258 pigs (PIC x Terminal Duroc, 8.2 kg, 6 weeks of age) were housed in a fully slatted-floor, environmentally controlled room. Individual pig body weights (BW) were measured, along with average daily feed intake (ADFI) every two weeks for the first six weeks, and then every three weeks for the final nine weeks. The treatment regimen consisted of formulations using: 1) Corn-soybean meal, 100% of lysine requirement; 2) Corn-soybean meal, 90% of lysine requirement; 3) SBM-DDGS (20% of diet)-synthetic amino acids at 100% of lysine requirement; 4) SBM-DDGS-synthetic amino acid-based diets formulated to 90% of lysine requirement. NE estimates were 2,502 kcal/kg and 2,342 kcal/kg for SBM and DDGS, respectively. The four diets were allotted to 44 pens (11 pens/diet), with six pigs per pen, in a randomized complete block design (RCBD). Performance and carcass data were subjected to analysis as an RCBD with pens as the experimental unit and dietary treatment as a fixed effect. Overall wean-to-finish performance variables, including average daily gain (ADG), feed disappearance (ADFI), and gain-to-feed ratio (G:F), did not show a statistically significant difference (P > 0.10) between treatment groups. Similarly, hot carcass weight, back fat, loin depth, and percent lean showed no statistical differences between dietary treatments (P > 0.10). In contrast to previous studies, both SBM and synthetic amino acids performed similarly and met the lysine needs of wean-finish pigs at 90% or 100% of the SID lysine requirement. Adjusting the Lysine:NE ratio for a higher NE in SBM did not alter pig performance in this trial.

Halbur, J., J. Lira-Silva, R. Samuel, R. Royall, R. Taler and E. Weaver. 2026. Optimizing Soybean Meal Utilization: Pig Performance Unchanged at Lower lysine:ne Ratios. ASAS Midwest Section Meeting. Abstract 166. https://doi.org/10.1093/jas/skag107.155