Depending on price, people may consider over-formulating soybean meal (SBM) in pig diets beyond essential amino acid requirements. Therefore, our objective was to evaluate high dietary SBM inclusion rates on grow-finish pig performance and carcass parameters. A total of 240 pigs (PIC 337 × Camborough; 22.4 ± 1.21 kg BW) were utilized in a 112-day study divided into four 28-day dietary phase periods. Sixty mixed-gender pens containing four pigs were randomly assigned to 1 of 5 dietary treatments with increasing soybean meal (SBM) levels. These included: Phase 1 at 26, 38, 57, 66, and 75%; Phase 2 at 19, 30, 40, 50, and 60%; Phase 3 at 15, 26, 35, 43, and 52%; and Phase 4 at 15, 21, 28, 35, and 43% SBM. Within each phase, all diets were corn-SBM based and formulated to meet or exceed amino acid requirement recommendations. Data were analyzed with a pen as the experimental unit, the treatment effect of SBM inclusion, followed by linear and quadratic contrasts for SBM inclusion. No negative health impacts were observed. Increasing SBM levels tended to impact the phase-1 ADG, (Linear P = 0.07; 901, 884, 850, 868, 814 g/d), reduced phase-1 ADFI, (Linear P = 0.03; 1.60, 1.58, 1.54, 1.50, 1.46 kg/d), and reduced ultrasound backfat thickness (BF), (Linear P < 0.001; 7.8, 7.2, 7.0, 6.7, 6.5 mm). In contrast, there were no significant differences in the overall grow-to-finish ADG (P = 0.76), ADFI (P = 0.53), or gain-to-feed ratio (P = 0.27). As expected, SID Lys intake increased (Linear P < 0.001; 21.7, 21.0, 26.9, 32.1, 38.3 g/d) and SID Lys efficiency (SID Lys intake relative to weight gain) reduced as SBM levels increased (Linear P < 0.001; 21.9, 21.5, 27.6, 32.3, 39.3 g/kg of gain). Moreover, increasing SBM levels reduced NE intake (Linear P = 0.03; 6,099, 5,860, 5,702, 5,629, 5,750 kcal/day). Interestingly, caloric efficiency tended to improve with increasing SBM (Linear P = 0.06; 5,906, 5,741, 5,602, 5,400, 5,644 kcal/kg of gain). Additionally, ultrasound at harvest indicated that pigs fed the lowest SBM diet (19%) had the highest BF, which progressively decreased with increasing SBM (Linear P < 0.01; 17.1, 16.1, 15.8, 15.1, 14.2 mm). No significant effects were observed on end body weight, hot carcass weight, carcass dressing percentage, carcass lean, carcass loin depth and area, and carcass backfat. These results suggest that feeding SBM above the requirement for meeting essential amino acids improved energy efficiency and reduced BF and NE intake without affecting growth performance. After adaptation to elevated levels of SBM in Phase 1, no evidence was found to suggest very high dietary SBM inclusion rates negatively impacted grow-finisher pig growth performance and health.

Lima, G., S. Lau, N. Vander Werff, C. Johnson, N. Gabler and D. Rosero. 2025. Determining the maximum inclusion rate of soybean meal in grow-to-finish pig diets. 2025 American Society of Animal Science Midwest Section meeting, Abstract 94.